SUMMARY

The following is a summary of information located elsewhere in this document. It does not contain all of the information that is important to you. Before you vote, you should give careful consideration to all of the information contained in this document and the information incorporated into this document by reference to fully understand the merger. See “Where You Can Find More Information” on page 102. Each item in this summary refers to the page where that subject is discussed in more detail.

General

Western Alliance Bancorporation, or Western Alliance, and Western Liberty Bancorp, or Western Liberty, have entered into an Agreement and Plan of Merger dated August 17, 2012, or the merger agreement. Pursuant to the terms of the merger agreement, Western Liberty will merge with and into Western Alliance, with Western Alliance surviving, or the merger. In connection with the merger, Western Liberty’s wholly owned subsidiary, Service1st Bank of Nevada, or Service1st, may merge with and into Bank of Nevada, a wholly owned subsidiary of Western Alliance, with Bank of Nevada surviving.

The Companies Involved in the Merger (page 37)

Western Alliance Bancorporation

One E. Washington Street

Phoenix, Arizona 85004

Tel: (602) 839-3500

Western Alliance, incorporated in the State of Nevada, is a multi-bank holding company headquartered in Phoenix, Arizona that provides full service banking and lending to locally owned businesses, professional firms, real estate developers and investors, local non-profit organizations, high net worth individuals and other consumers through its three wholly owned subsidiary banks: Bank of Nevada, operating in Southern Nevada, Western Alliance Bank, operating in Arizona and Northern Nevada, and Torrey Pines Bank, operating in California. On December 31, 2010, Western Alliance merged its former Alta Alliance Bank subsidiary into its Torrey Pines Bank subsidiary, and its former First Independent Bank of Nevada subsidiary into its Alliance Bank of Arizona subsidiary. As part of the latter merger, Alliance Bank of Arizona was renamed Western Alliance Bank doing business as Alliance Bank of Arizona (in Arizona) and First Independent Bank (in Nevada). In addition, Western Alliance’s non-bank subsidiaries, Shine Investment Advisory Services, Inc. and Western Alliance Equipment Finance, offer an array of financial products and services, including financial planning, investments, and equipment leasing nationwide. Western Alliance divested its wholly owned subsidiary Premier Trust, Inc. as of September 1, 2010. On a consolidated basis, as of June 30, 2012, Western Alliance had approximately $7.16 billion in assets, $5.16 billion in total loans, $6 billion in deposits and $672.1 million in stockholders’ equity.

Western Liberty Bancorp

8363 W. Sunset Road, Suite 350

Las Vegas, Nevada 89113

Tel: (702) 966-7400

Western Liberty is a Delaware bank holding company headquartered in Las Vegas, Nevada. Western Liberty Bancorp owns two subsidiaries: Service1st Bank of Nevada, or Service1st, and Las Vegas Sunset Properties. Service1st, a Nevada-chartered bank, operates as a traditional community bank and provides a full range of deposit, lending and other banking services to locally owned business, professional firms, individuals

and other customers from its headquarters and two retail banking facilities located in the greater Las Vegas area. Unrelated to the proposed merger, in mid-June 2012, Service1st sought regulatory approval for the closure of its branch located at 8965 South Eastern Avenue, Las Vegas. Service1st has since received such regulatory approval and expects to close the branch in mid-September 2012. Las Vegas Sunset Properties was established in 2011 for the purpose of owning and managing nonperforming and sub performing assets of Service1st. On a consolidated basis, as of June 30, 2012, Western Liberty had approximately $198.7 million in assets, $104.8 million in total loans, $124.3 million in deposits and $73.7 million in stockholders’ equity.

Merger Consideration (page 78)

Cash or Stock Consideration. The merger agreement provides that Western Liberty stockholders will have the right, with respect to each of their shares of Western Liberty common stock, to elect to receive, subject to certain proration and other provisions as described below, either (i) 0.4341 of a share of Western Alliance common stock, the stock consideration, or (ii) $4.02 in cash, without interest, the cash consideration, and together with the stock consideration, the merger consideration. The cash consideration and stock consideration have been calculated based on the number of shares of Western Liberty common stock outstanding as of August 17, 2012 and assuming the conversion of outstanding Western Liberty restricted stock units, the vesting of Western Liberty restricted stock awards and that no Western Liberty stock options are exercised. The actual stock consideration and cash consideration will be determined based on the number of shares of Western Liberty common stock issued and outstanding as of the effective time of the merger.

Western Alliance will issue no more than 2,966,322 shares of common stock, subject to potential adjustment under certain termination provisions of the merger agreement and for tax purposes, as set forth in the merger agreement and under the headings “The Merger Agreement—Termination of the Merger Agreement” and “The Merger Agreement—Potential Adjustment of the Merger Consideration,” and will pay no more than $27.5 million in cash under the terms of the merger agreement. If the total merger consideration exceeds the amount set forth in the previous sentence (including any cash paid in connection with the cancellation of outstanding and unexercised stock options for which the option holders have not made an exercise election (as more fully described under “The Merger Agreement—Merger Consideration” beginning on page 78) and after giving effect to dissenting shares as if they had been converted into the right to receive the merger consideration), then the total merger consideration shall be reduced on a pro rata basis to the aggregate amount set forth in the preceding sentence.

You will have the opportunity to elect the form of consideration to be received for your shares, subject to proration and allocation procedures set forth in the merger agreement which may result in your receiving a portion of the merger consideration in a form other than that which you elected.

Election Procedures for Stockholders; Surrender of Stock Certificates (page 80)

If you own Western Liberty common stock, you will soon receive under separate cover an election form that you may use to indicate whether your preference is to receive cash or shares of Western Alliance common stock. The election deadline will be 5:00 p.m., New York time, on                     , 2012, the day prior to the date of the special meeting, or the election deadline. To make an election, a holder of Western Liberty common stock must submit a properly completed election form and return it, together with all stock certificates, so that the form and certificates are actually received by the exchange agent at or before the election deadline in accordance with the instructions on the election form. Western Liberty stockholders will be unable to sell their Western Liberty common stock from the time when the election is made until the merger is completed.

Non-Electing Western Liberty Stockholders (page 78)

Western Liberty stockholders who make no election to receive cash or Western Alliance common stock in the merger or who do not make a valid election, will be deemed not to have made an election. Stockholders not

making an election may be paid in cash, Western Alliance common stock or a mix of cash consideration and stock consideration depending on, and after giving effect to, the number of valid cash elections and stock elections that have been made by other Western Liberty stockholders using the proration adjustment described below.

Election Limitations and Proration (page 79)

The total number of shares of Western Liberty common stock to be converted into Western Alliance common stock in the merger will be 50% of the outstanding shares of Western Liberty common stock on a fully diluted basis as of the effective time. The remaining shares of Western Liberty common stock will be converted into cash. Therefore, elections are subject to certain proration and other provisions to preserve this requirement regarding the number of shares of Western Liberty common stock to be converted into Western Alliance common stock in the merger. The proportion of stock and cash to be issued in the merger is also subject to potential adjustment for tax purposes as set forth in the merger agreement and under the heading “The Merger Agreement—Potential Adjustment of the Merger Consideration.” As a result, if you elect to receive only cash or only stock, you may nevertheless receive a mix of cash and stock.

Proration if Too Much Stock is Elected. If the Western Liberty stockholders’ election would result in more than 50% of the outstanding shares of Western Liberty common stock to be exchanged for shares of Western Alliance common stock, then all Western Liberty stockholders who elected to receive cash consideration or did not make an election shall receive cash consideration, and all stockholders who have elected to receive stock consideration will receive the following:

Proration if Too Much Cash is Elected. If the Western Liberty stockholders’ election would result in fewer than 50% of the outstanding shares of Western Liberty common stock to be exchanged for shares of Western Alliance common stock, then all Western Liberty stockholders who elected to receive stock consideration will receive stock consideration, and those stockholders who have elected to receive cash consideration or have made no election will receive the following:

Treatment of Stock Options and Restricted Stock Awards (page 79)

Immediately prior to the effective time of the merger, or the effective time, each outstanding and unexercised option granted by Western Liberty will become fully vested and exercisable. Each option holder may elect to exercise any such option in accordance with the other terms of such option, contingent on the consummation of the merger, and may elect to receive, for any shares of Western Liberty common stock acquired in such election, cash consideration, stock consideration, or a combination thereof in accordance with the terms of the merger agreement and subject to the proration provisions thereof. At the effective time, any outstanding and unexercised option for which the option holder has not made an exercise election will be cancelled and in exchange for such cancellation the optionee will receive an amount of cash, without interest, equal to the product of (i) the excess, if any, of the per share cash consideration over the exercise price per share of such option and (ii) the number of shares of Western Liberty common stock subject to such option, which cash payment shall be treated as compensation and shall be net of any applicable federal or state withholding tax. It is anticipated that no such cash payments will be made at the effective time because all of the outstanding options to acquire Western Liberty common stock are currently significantly out-of-the-money. At the effective time, if an exercise election is not made for an option and the exercise price of such option exceeds the per share cash consideration, the option shall be cancelled without payment.

At the effective time, all outstanding unvested shares of Western Liberty common stock granted in the form of “restricted stock” awards and all grants in the form of “restricted stock units” made by Western Liberty that are convertible into shares of Western Liberty common stock will become vested rights to receive the merger consideration, subject to proration.

Election Procedures for Holders of Western Liberty Options, Restricted Stock and Restricted Stock Units (page 82)

If you own options to purchase shares of Western Liberty common stock or you hold restricted stock awards of Western Liberty common stock or grants in the form of restricted stock units, you will soon receive under separate cover an election form that you may use to make an election regarding the merger consideration to be received for any such awards or grants you hold or an exercise election with respect to your options and the form of merger consideration to be received for shares of Western Liberty common stock acquired in such election. The election deadline will be the same as for elections with respect to shares of Western Liberty common stock, which is 5:00 p.m., New York City time, on                     , 2012, the date prior to the date of the special meeting. To make an election, a holder must submit a properly completed election form and return it so that the form is actually received by American Stock Transfer & Trust Company, LLC at or before the election deadline in accordance with the instructions on the election form.

Material U.S. Federal Income Tax Consequences of the Merger (page 74)

The merger is intended to qualify for U.S. federal income tax purposes as a “reorganization” within the meaning of Section 368(a) of the Internal Revenue Code of 1986, as amended, or the Code. Therefore, for U.S. federal income tax purposes, as a result of the merger, it is expected that a U.S. holder of shares of Western Liberty common stock generally will only recognize gain (but not loss) in an amount not to exceed the cash (if any) received as part of the merger consideration and will recognize gain or loss if such holder received the entirety of its consideration in cash or with respect to any cash received in lieu of fractional shares of Western Alliance common stock.

Western Liberty stockholders are urged to read the discussion in the section entitled “Material U.S. Federal Income Tax Consequences of the Merger” beginning on page 74 and to consult their tax advisors for a full explanation of the tax consequences of the merger.

Western Liberty Board of Directors Recommends Approval (page 43)

After careful consideration of the various factors, including those set forth under the heading “The Merger—Western Liberty’s Reasons for the Merger and Recommendation of Western Liberty’s Board of Directors” beginning on page 52, the Western Liberty Board of Directors has determined that the merger agreement, the merger and the transactions contemplated by the merger agreement are advisable, fair to, and in the best interests of Western Liberty and its stockholders. Accordingly, the Western Liberty Board of Directors unanimously recommends that Western Liberty stockholders vote:

The merger is not conditioned on the receipt of stockholder approval (on an advisory, non-binding basis) of the “golden parachute” arrangements proposal or the proposal to approve adjournments or postponements of the special meeting.

Opinion of Financial Advisor to Western Liberty (page 55)

In connection with the proposed merger, Western Liberty’s financial advisor, Sandler O’Neill & Partners, L.P., or Sandler O’Neill delivered to the Western Liberty Board of Directors its fairness opinion orally, which was subsequently confirmed in writing, that, as of the date of the opinion, and subject to the limitations, qualifications, factors, and assumptions set forth therein, the per share consideration to be paid to the holders of Western Liberty’s common stock was fair to the holders of Western Liberty common stock from a financial point of view. The full text of the written opinion is attached as Appendix C to this document and is incorporated herein by reference. The written opinion sets forth, among other things, the assumptions made, procedures followed, factors considered and limitations on the review undertaken by Sandler O’Neill in rendering its opinion. The opinion is directed to the Board of Directors of Western Liberty in connection with its consideration of the merger and does not constitute a recommendation to any stockholder of Western Liberty as to how such stockholder should vote at any meeting of stockholders called to consider and vote upon the merger. The opinion is directed only to the fairness, from a financial point of view, of the per share consideration to holders of Western Liberty common stock and does not address the underlying business decision of Western Liberty to engage in the merger, the relative merits of the merger as compared to any other alternative business strategies that might exist for Western Liberty or the effect of any other transaction in which Western Liberty might engage.

Dissenters’ Appraisal Rights (page 69)

Under Delaware law, you are entitled to dissenters’ rights of appraisal in connection with the merger, provided that you meet all of the conditions set forth in Section 262 of the Delaware General Corporation Law.

In particular, under Delaware law, appraisal rights are only available if, among other things, stockholders are required to accept cash for their shares (other than cash in lieu of fractional shares). Therefore, with respect to any shares of Western Liberty common stock for which you did not elect to receive cash merger consideration, but would be required under the merger agreement to receive cash merger consideration (other than cash in lieu of fractional shares of Western Liberty common stock), you may have the right, if you do not vote in favor of the merger agreement, in lieu of receiving the cash merger consideration for those shares, to obtain payment in cash for the “fair value” of those shares as determined by the Delaware Chancery Court. It is possible that the fair value as determined by the Delaware Chancery Court may be more or less than, or the same as, the merger consideration. Western Liberty reserves the right to take the position that appraisal may only be sought with respect to shares described in the second sentence of this paragraph, and may not be exercised with respect to any shares as to which cash was elected or stock was received.

To exercise appraisal rights, you must follow the strict procedures prescribed by Section 262 of the Delaware General Corporation Law. For additional information, please see the section titled “The Merger—Dissenters’ Appraisal Rights” beginning on page 69. In addition, the full text of Section 262 of the Delaware General Corporation Law is included as Appendix B to this proxy statement/prospectus.

Differences in the Rights of Stockholders (page 92)

Western Alliance is a Nevada corporation and Western Liberty is a Delaware corporation. The Western Alliance articles of incorporation and bylaws contain provisions that are different from the Western Liberty certificate of incorporation and bylaws. Upon completion of the merger, Western Liberty stockholders who receive stock consideration in the merger will become stockholders of Western Alliance, and their rights will be governed by the Nevada Revised Statutes and Western Alliance’s articles of incorporation and bylaws. No change to Western Alliance’s articles of incorporation or bylaws will be made as a result of the completion of the merger. For a discussion of certain differences among the rights of Western Alliance stockholders and Western Liberty stockholders, see “Differences in the Rights of Stockholders” beginning on page 92.

Interests of Western Liberty Directors and Executive Officers in the Merger That are Different From Yours (page 64)

In considering Western Liberty’s Board of Directors recommendation to vote in favor of the merger agreement proposal and the “golden parachute” arrangements proposal, you should be aware that Western Liberty’s executive officers and directors have interests in the merger that may be different from, or in addition to, the interests of Western Liberty stockholders generally. Western Liberty’s Board of Directors was aware of these interests and considered them, among other matters, when it approved the merger agreement and the merger and the other transactions contemplated thereby. For more information see “The Merger—Interests of Western Liberty Executive Officers and Directors in the Merger That are Different From Yours” beginning on page 64.

Regulatory Approvals We Must Obtain to Complete the Merger (page 72)

For the merger to take place, we need to receive the regulatory approvals of the Board of Governors of the Federal Reserve System and the Nevada Financial Institutions Division. For the bank merger to take place, we need to receive the approval of the Federal Deposit Insurance Corporation and the Nevada Financial Institutions Division. We have filed applications with these regulators.

As of the date of this document, we have not yet received the required approvals. We cannot be certain when or if we will obtain them.

No Solicitation of Alternative Transactions (page 86)

Western Liberty has agreed not to initiate, solicit, encourage or knowingly facilitate the submission of any proposals from third parties regarding acquiring Western Liberty or its businesses. In addition, Western Liberty has agreed not to engage in discussions or negotiations with or provide confidential information to a third party regarding acquiring Western Liberty or its businesses. However, if Western Liberty receives an acquisition proposal from a third party that did not result from solicitation in violation of its obligations under the merger agreement prior to the date of the special meeting of Western Liberty stockholders, Western Liberty may participate in discussions with, or provide confidential information to, such third party if, among other steps, the Western Liberty Board of Directors concludes in good faith that the failure to take such actions would or would be reasonably likely to result in a violation of its fiduciary duties under applicable law.

Termination of the Merger Agreement (page 88)

The merger agreement may be terminated prior to the effective time of the merger by either Western Alliance or Western Liberty if:

Additionally, Western Alliance may terminate the merger agreement if:

Western Liberty may terminate the merger agreement if:

Expenses; Breakup Fee (page 89)

Fees and Expenses Payable by Western Alliance. Western Alliance has agreed to reimburse Western Liberty up to $400,000 for its documented, reasonable costs and expenses incurred in connection with the merger agreement and the transactions contemplated thereby, if the merger agreement is terminated by Western Liberty due to Western Alliance’s material (not willful) breach of a representation, warranty, covenant or other agreement contained in the merger agreement.

Fees and Expenses Payable by Western Liberty. Western Liberty has agreed to reimburse Western Alliance up to $400,000 for its documented, reasonable costs and expenses incurred by Western Alliance in connection with the merger agreement and the transactions contemplated thereby, plus a breakup fee of $2.0 million, under any of the following circumstances:

Additionally, Western Liberty has agreed to reimburse Western Alliance up to $400,000 for its documented, reasonable costs and expenses up to $400,000 incurred by Western Alliance and its affiliates in connection with the merger agreement and the transactions contemplated thereby, if the merger agreement is terminated by Western Alliance due to (i) Western Liberty’s material (not willful) breach of a representation, warranty, covenant or other agreement contained in the merger agreement or (ii) the failure of the representations and warranties of Western Liberty with respect to its capitalization to be accurate in any material respect.

Support Agreement (page 91)

On August 17, 2012, concurrently with the execution of the merger agreement, executive officers and directors of Western Liberty who currently own approximately 5.9% of Western Liberty’s common stock, entered into a support agreement with Western Alliance pursuant to which the executive officers and directors, among other things and subject to the terms and conditions thereof, agreed to vote in favor of the approval of the merger agreement, the merger and the other transactions contemplated by the merger agreement and against any alternative business combination transaction. A copy of the support agreement is attached to this proxy statement/prospectus at Appendix D.

Listing of Western Alliance Common Stock (page 91)

Western Alliance has agreed to use its reasonable best efforts to cause the shares Western Alliance common stock that are to be issued pursuant to the merger to be approved for listing on the NYSE prior to the effective time of the merger.

Conditions to the Merger (page 82)

Each party’s obligations to effect the merger are subject to the satisfaction or waiver of mutual conditions, including, among other things, the following:

Share Information and Market Prices (page 35)

Western Alliance’s common stock is traded on the NYSE under the trading symbol “WAL” and Western Liberty’s common stock is traded on the NASDAQ Global Market under the trading symbol “WLBC.” The table below presents the per share closing prices of Western Alliance’s and Western Liberty’s common stock as of August 16, 2012, the last trading date before execution of the merger agreement and                     , 2012, the last practicable day before the date of this proxy statement/prospectus. The table also shows the implied value per share of Western Alliance common stock which is calculated by valuing the Western Alliance common stock at the relevant date below per share and multiplying this value by the assumed exchange ratio of 0.4341. For more information about the exchange ratio, see “The Merger—Merger Consideration,” and for more information about the stock prices and dividends of Western Alliance and Western Liberty, see “Comparative Per Share Market Price and Share Information.”

The market price of Western Alliance’s common stock will fluctuate between the date of this proxy statement/prospectus and the date on which the merger takes place. Western Liberty’s stockholders are advised to obtain current market quotations for Western Alliance’s common stock. The total dollar value of the Western Alliance common stock that a Western Liberty stockholder will be entitled to receive as a result of the merger may be significantly higher or lower than its current value. No assurance can be given as to the market price of Western Alliance’s common stock at the time of the merger.

The Special Meeting (page 38)

Date, Time and Place (page 38). The special meeting of Western Liberty stockholders will be held at             , local time, on                     , 2012, at Western Liberty’s principal executive offices at 8363 W. Sunset Road, Suite 350, Las Vegas, Nevada 89113.

Purpose of the Special Meeting (page 38). At the special meeting, Western Liberty stockholders will be asked to:

Record Date; Shares Entitled to Vote (page 38). Western Liberty has fixed the close of business on                     , 2012 as the record date, for determining the Western Liberty stockholders entitled to receive notice of and to vote at the special meeting. Only holders of record of Western Liberty common stock on the record date are entitled to receive notice of and vote at the special meeting, and any adjournment or postponement thereof.

Each share of Western Liberty common stock is entitled to one vote on each matter brought before the meeting. On the record date, there were              shares of Western Liberty common stock issued and outstanding.

Quorum Requirement (page 38). Under Delaware law and Western Liberty’s bylaws, a quorum of Western Liberty’s stockholders at the special meeting is necessary to transact business. The presence of holders representing a majority of Western Liberty’s common stock issued and outstanding on the record date and entitled to vote at the special meeting will constitute a quorum for the transaction of business at the special meeting.

All of the shares of Western Liberty common stock represented in person or by proxy at the special meeting, including abstentions, will be treated as present for purposes of determining the presence or absence of a quorum at the special meeting.

Votes Required to Approve the Proposals (page 39). Western Liberty’s proposals require different percentages of votes in order to approve them:

The vote on the “golden parachute” arrangements proposal is not a condition to the merger and is a vote separate and apart from the vote to approve the merger agreement. Because the vote on the “golden parachute” arrangements proposal is advisory in nature only, it will not be binding on Western Liberty. Therefore, if the other requisite stockholder approvals are obtained and the merger is completed, the amounts payable in

connection with the “golden parachute” arrangements will still be paid as long as any other conditions applicable thereto occur.

Failure to Vote; Abstentions and Broker Non-Votes (page 39). No vote will be cast on any proposal at the special meeting on behalf of any stockholder of record who does not cast a vote on such proposal. However, if the stockholder properly submits a proxy prior to the special meeting, such stockholder’s shares of common stock will be voted as he or she directs. If he or she submits a proxy but no direction is otherwise made, the shares of common stock will be voted “FOR” the merger agreement proposal, “FOR” the “golden parachute” arrangements proposal and “FOR” the approval of any adjournments of the special meeting, if necessary, for the purpose of soliciting additional proxies in favor of the foregoing proposals.

Failure to vote will have the same effect as a vote “AGAINST” the merger agreement proposal.

Shares held by a Western Liberty stockholder who indicates on an executed proxy card that he or she wishes to abstain from voting will count toward determining whether a quorum is present and will have the same effect as a vote “AGAINST” the merger agreement proposal, the “golden parachute” arrangements proposal and the proposal to approve of any adjournments of the special meeting, if necessary, for the purpose of soliciting additional proxies in favor of the foregoing proposals.

If a broker non-vote occurs, the broker non-vote will count for purposes of determining a quorum. A broker non-vote will have the same effect as a vote “AGAINST” the merger agreement proposal, the golden parachute arrangements proposal and the proposal to permit the proxies to adjourn or postpone the special meeting.

For more information see “The Special Meeting—Failure to Vote; Abstentions and Broker Non-Votes” beginning on page 39.

Solicitation of Proxies (page 41). This solicitation is made on behalf of Western Liberty’s Board of Directors and Western Liberty will pay the costs of soliciting and obtaining proxies, including the cost of reimbursing banks and brokers for forwarding proxy materials to their principals. For more information see “The Special Meeting—Solicitation of Proxies” beginning on page 41.

Revocation of Proxies (page 41). You may revoke your proxy at any time prior to the close of voting at the special meeting by doing any one of the following: (1) complete, sign, date and submit another proxy (a properly executed, valid proxy will revoke any previously submitted proxies); (2) re-vote by telephone or on the Internet; (3) provide written notice of revocation to Western Liberty’s Chief Financial Officer; or (4) attend the special meeting and vote in person. For more information see “The Special Meeting—Revocability of Proxies” beginning on page 41.

Comparative Unaudited Per Share Data

The following table shows information, at and for the periods indicated, about Western Alliance’s and Western Liberty’s historical book value per share and earnings per share. The table also contains pro forma information that reflects the merger of Western Alliance and Western Liberty using the purchase method of accounting. The combined company and pro forma equivalent information has been provided assuming that, on an aggregate basis, 50% of the shares of Western Liberty common stock are exchanged for stock consideration, as required by the merger agreement. The cash consideration is $4.02 per share, and the stock consideration is 0.4341 of a share of Western Alliance common stock. The table below reflects an exchange ratio of 0.4341. The cash consideration and stock consideration have been calculated based on the number of shares of Western Liberty common stock outstanding as of August 17, 2012 and assuming the conversion of outstanding Western Liberty restricted stock units, the vesting of Western Liberty restricted stock awards and that no Western Liberty

stock options are exercised. The actual stock consideration and cash consideration will be determined based on the number of shares of Western Liberty common stock issued and outstanding as of the effective time.

Neither Western Alliance nor Western Liberty has ever paid a cash dividend on its common stock and neither company anticipates paying any cash dividends in the foreseeable future.

You should read the information in the following table in conjunction with Western Alliance’s consolidated financial statements and related notes for the years ended December 31, 2009 through 2011 and for the six months ended June 30, 2012 and 2011 that are incorporated in this proxy statement/prospectus and from which this information is derived. You should not rely on the pro forma information as being indicative of the results that Western Alliance will achieve in the transaction. See also “Where You Can Find More Information” on page 102.

QUESTIONS AND ANSWERS ABOUT THE MERGER

We are delivering this proxy statement/prospectus to you as both a proxy statement of Western Liberty and a prospectus of Western Alliance. It is a proxy statement because the Western Liberty’s Board of Directors is soliciting proxies from its stockholders to vote on the approval (i) of the merger agreement; (ii) on an advisory (non-binding) basis, of the compensatory arrangements between Western Liberty and its named executive officers providing for compensation in connection with the merger and the agreements and understandings pursuant to which such compensation may be paid or become payable at a special meeting of stockholders; and (iii) adjournments of the special meeting, if necessary, for the purpose of soliciting additional proxies in favor of the foregoing proposals, and your proxy will be used at the special meeting or at any adjournment or postponement of the special meeting. This document is a prospectus because Western Alliance will issue Western Alliance common stock to the Western Liberty common stockholders who receive stock consideration in the merger and this prospectus contains information about that common stock.

You will have the opportunity to elect the form of consideration to be received for your shares, subject to proration and allocation procedures set forth in the merger agreement which may result in your receiving a portion of the merger consideration in a form other than that which you elected.

Western Alliance may opt to increase the exchange ratio in specific circumstances where Western Liberty could otherwise terminate the merger agreement and likewise, Western Liberty may opt to decrease the exchange ratio in specific circumstances where Western Alliance could otherwise terminate the merger agreement. For more information regarding these termination rights and the adjustments that may result to the merger consideration, see “The Merger—Termination of the Merger Agreement” on page 88 for more information.

To facilitate the merger’s compliance with the “continuity of interest” requirement for tax-free reorganizations under the Code, the merger consideration is subject to potential adjustment to ensure that, for U.S. federal income tax purposes, the value of the total stock consideration paid to Western Liberty stockholders is no less than 42.5% of the value of the total merger consideration. For more information regarding the potential adjustments that may result to the merger consideration for U.S. federal income tax purposes, see the factors discussed in “Risk Factors” beginning on page 23 and “The Merger Agreement—Potential Adjustment of the Merger Consideration” beginning on page 91.

If the merger is not completed, any options which have been so exercised will remain outstanding, subject to their original vesting schedules. At the effective time, any outstanding and unexercised option for which an exercise election has not been made will be cancelled and in exchange for such cancellation the optionee will receive an amount of cash, without interest, equal to the product of the (i) excess, if any, of the per share cash consideration to be paid by Western Alliance over the exercise price per share of such option and (ii) number of shares of Western Liberty common stock subject to such option, which cash payment will be treated as compensation and will be net of any applicable federal or state withholding tax. At the effective time, any option for which no exercise election is made the exercise price of which exceeds the per share cash consideration to be paid by Western Alliance will be cancelled without payment.

At the effective time, all outstanding unvested shares of Western Liberty common stock granted in the form of “restricted stock” awards and all grants in the form of “restricted stock units” made by Western Liberty that are convertible into shares of Western Liberty common stock will become vested rights to receive the merger consideration, subject to proration.

If you are an option holder and do not complete and return your election form, you will receive an amount of cash, without interest, equal to the product of (i) the excess, if any, of the cash consideration over the exercise price per share of such option and (ii) the number of shares of Western Liberty common stock subject to such option, which cash payment shall be treated as compensation and shall be net of any applicable federal or state withholding tax. At the effective time, if an election is not made for an option and the exercise price of such option exceeds the cash consideration, the option shall be cancelled without payment. If you hold restricted stock awards of Western Liberty common stock or restricted stock units and you do not complete and return your election form, you may be paid in cash, Western Alliance common stock or a mix of cash consideration and stock consideration depending on, and after giving effect to, the number of valid cash elections and stock elections that have been made by other Western Liberty stockholders using the proration adjustment described herein and set forth in the merger agreement.

If you are a Western Liberty optionholder, you should complete and return the election form with respect to your options to American Stock Transfer & Trust Company, LLC according to the instructions printed on the form.

When the law permits, Western Alliance or Western Liberty could decide to complete the merger even though one or more of these conditions has not been met. We cannot be certain when, or if, the conditions to the merger will be satisfied or waived, or that the merger will be completed.

To exercise appraisal rights, Western Liberty stockholders must strictly follow the procedures prescribed by Delaware law. These procedures are summarized under the section entitled “The Merger—Dissenters’ Appraisal Rights” beginning on page 69. In addition, the text of the applicable appraisal rights provisions of Delaware law is included as Appendix B to this proxy statement/prospectus.

A copy of the merger agreement and any of the documents incorporated by reference in this proxy statement/prospectus will be provided to you promptly without charge if you call or write to Dale Gibbons, Chief Financial Officer, Western Alliance Bancorporation, One E. Washington Street, Suite 1400, Phoenix, Arizona 85004, Telephone: 602-389-3500 or Patricia A. Ochal, Chief Financial Officer of Western Liberty, 8363 W. Sunset Road, Suite 350, Las Vegas, Nevada 89113, at (702) 966-7400. The merger agreement and the documents incorporated herein by reference have been previously filed with the SEC. See “Where You Can Find More Information” on page 102.

CAUTIONARY NOTE CONCERNING FORWARD-LOOKING STATEMENTS

This proxy statement/prospectus, including information included or incorporated by reference in this proxy statement/prospectus, may contain forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. These forward-looking statements include, but are not limited to, statements about the benefits of the merger between Western Alliance and Western Liberty, including future financial and operating results and performance; statements about Western Alliance and Western Liberty’s plans, objectives, expectations and intentions with respect to future operations, products and services; and other statements identified by words such as “expects,” “anticipates,” “intends,” “plans,” “believes,” “seeks,” “estimates,” “will,” “should,” “may” or words of similar meaning. These forward-looking statements are based upon the current beliefs and expectations of Western Alliance and Western Liberty’s management and are inherently subject to significant business, economic and competitive uncertainties and contingencies, many of which are difficult to predict and generally beyond the control of Western Alliance and Western Liberty. In addition, these forward-looking statements are subject to assumptions with respect to future business strategies and decisions that are subject to change. Actual results may differ materially from the anticipated results discussed in these forward-looking statements.

The following factors, among others, could cause actual results to differ materially from the anticipated results or other expectations expressed in the forward-looking statements:

Additional factors that could cause Western Alliance’s and Western Liberty’s results to differ materially from those described in the forward-looking statements can be found in Western Alliance’s and Western Liberty’s filings with the Securities and Exchange Commission, including Western Alliance’s and Western Liberty’s respective Annual Reports on Form 10-K for the fiscal year ended December 31, 2011, as, in the case of Western Liberty, amended, and their respective Quarterly Reports on Form 10-Q for the quarters ending March 30, 2012 and June 30, 2012.

You are cautioned not to place undue reliance on the forward-looking statements, which speak only as of the date of this proxy statement/prospectus or the date of any document incorporated by reference in this proxy statement/prospectus. All subsequent written and oral forward-looking statements concerning the merger or other matters addressed in this proxy statement/prospectus and attributable to Western Alliance and Western Liberty or any person acting on their behalf are expressly qualified in their entirety by the cautionary statements contained or referred to in this section. Except to the extent required by applicable law or regulation, Western Alliance and Western Liberty undertake no obligation to update these forward-looking statements to reflect events or circumstances after the date of this proxy statement/prospectus or to reflect the occurrence of unanticipated events.