MTS

PROXY STATEMENT

Introduction

The Board of Directors of Montgomery Street Income Securities, Inc. (the “Fund”) is soliciting proxies for use at the Annual Meeting of Stockholders (the “Annual Meeting”). The Annual Meeting will be held at 4 Embarcadero Center, 22nd Floor, San Francisco, California, on Tuesday, July 23, 2013 at 10:00 a.m. (Pacific time). The Board of Directors also is soliciting proxies for use at any adjournment or postponement of the Annual Meeting. This Proxy Statement is furnished in connection with this solicitation. To obtain directions to the Annual Meeting, please call Jackson Fund Services, a division of Jackson National Asset Management, LLC, the Fund’s administrator (the “Administrator”), toll-free at (866) 255-1935.

Important Notice Regarding the Internet Availability of Proxy and Other Materials for the Annual Meeting

This Proxy Statement and the accompanying Notice of Annual Meeting of Stockholders and form of proxy card also are available on the Fund’s website at www.montgomerystreetincome.com.

You may, without charge, view the annual report of the Fund for the fiscal year ended December 31, 2012 in the “Financial Reports” tab on the Fund’s website at www.montgomerystreetincome.com or request a copy of the annual report or copies of any subsequent shareholder report by calling toll-free (877) 437-3938 or writing the Fund care of Computershare Shareowner Services LLC, P.O. Box 43006, Providence, Rhode Island 02940-3006.

Voting Information

The Fund may solicit proxies by mail, telephone, telegram, and personal interview. Computershare Fund Services, 280 Oser Avenue, Hauppauge, New York 11788, has been engaged to assist in the solicitation of proxies for the Fund, at an estimated cost of $5,000 plus expenses. In addition, the Fund may request personnel of the Fund’s Administrator to assist in the solicitation of proxies for no separate compensation. It is anticipated that the Fund will request brokers, custodians, nominees, and fiduciaries who are record owners of stock to forward proxy materials to their principals and obtain authorization for the execution of proxies. Upon request, the Fund will reimburse the brokers, custodians, nominees, and fiduciaries for their reasonable expenses in forwarding proxy materials to their principals. The Fund will bear the cost of soliciting proxies.

You may revoke the enclosed proxy at any time insofar as it has not yet been exercised by the appointed proxies. You may revoke the enclosed proxy by the following methods:

Montgomery Street Income Securities, Inc.

c/o Proxy Tabulator

P.O. Box 18011

Hauppauge, NY 11788-8811;

In order to obtain the quorum necessary to transact business, a majority of the shares entitled to be voted must have been received by proxy or be present at the Annual Meeting. Proxies that are marked to withhold voting, as well as proxies returned by brokers or others who have not received voting instructions and do not have discretion to vote for their clients (“broker non-votes”), will be counted towards this quorum. Withheld votes and broker non-votes will not be counted in favor of, but will have no other effect on, the election of Directors. Broker non-votes are not likely to be relevant to the Annual Meeting because the New York Stock Exchange currently considers an uncontested election of Directors to be routine and within the discretion of brokers to vote if customer instructions are not received.

In the event that the necessary quorum to transact business or the vote required to elect the proposed nominees is not obtained at the Annual Meeting, the persons named as proxies on the enclosed proxy card may propose one or more adjournments of the Annual Meeting to permit, in accordance with applicable law, further solicitation of proxies. Any such adjournment as to a matter will require the affirmative vote of the holders of a majority of the shares present in person or by proxy at the session of the Annual Meeting to be adjourned. The persons named as proxies on the enclosed proxy card will vote FOR any such adjournment those proxies which they are entitled to vote in favor of the proposal for which further solicitation of proxies is to be made. They will vote AGAINST any such adjournment those proxies required to be voted against such proposal.

The record date for determination of stockholders entitled to receive notice of the Annual Meeting and to vote at the Annual Meeting or any adjournments or postponements thereof was May 1, 2013 at 5:00 p.m. (Eastern time) (the “Record Date”).

As of the Record Date, there were issued and outstanding 10,369,675 shares of common stock of the Fund, constituting all of the Fund’s then outstanding securities. Each share of common stock is entitled to one vote.

Security Ownership

The following table sets forth for each Director of the Fund, the Principal Executive and Principal Financial Officers of the Fund, and the Directors and Executive Officers of the Fund as a group as of March 31, 2013 the amount of shares beneficially owned in the Fund, the dollar range of securities owned in the Fund, and the aggregate dollar range of all shareholdings in all funds overseen by each Director in the same family of investment companies. Each Director’s, the Principal Executive Officer’s and the Principal Financial Officer’s individual beneficial shareholdings in the Fund constituted less than 1% of the outstanding shares of the Fund; and, as a group, the Directors and Executive Officers owned beneficially less than 1% of the outstanding shares of the Fund.

At its April 23, 2013 meeting, the Board adopted a share ownership policy whereby each Director is normally required to beneficially own Fund shares of at least $100,000 based on the market value of the shares. In the case of a new Director, and of a Director whose investment falls below $90,000 due to a decline in the market value of the shares, the policy requires the Director to invest at least 50% of the Director’s retainer and meeting fees until the Director meets the minimum investment threshold.

To the Fund’s knowledge, as of December 31, 2012, the following entities owned beneficially more than 5% of the Fund’s outstanding shares.

Section 16(a) Beneficial Ownership Reporting Compliance

Section 16(a) of the Securities Exchange Act of 1934, as amended (the “1934 Act”), and Section 30(h) of the Investment Company Act of 1940, as amended (the “1940 Act”), as applied to a closed-end fund, require a fund’s officers and directors, investment adviser, affiliated persons of the investment adviser, and persons who beneficially own more than ten percent of a registered class of the fund’s outstanding securities (“Reporting Persons”) to file reports of ownership of the fund’s securities and changes in such ownership with the SEC and any exchange on which the fund’s securities are traded. Such persons are required by SEC regulations to furnish the fund with copies of all such reports.

Based on a review of reports filed by the Fund’s Reporting Persons, and written representations by the Reporting Persons that no year-end reports were required for such persons, all filings required by Section 16(a) of the 1934 Act for the fiscal year ended December 31, 2012 were timely.

PROPOSAL: ELECTION OF DIRECTORS

At the Annual Meeting, stockholders will be asked to elect four individuals to constitute the Board of Directors of the Fund. Each Director so elected will hold office until the next annual meeting or until the election and qualification of a successor. The four individuals listed below under “Information Concerning Nominees” were nominated for election as Directors of the Fund by the Fund’s present Board of Directors. Each of the nominees is currently a Director of the Fund and was elected to serve as a Director at the 2012 Annual Meeting of Stockholders.

The persons named proxies on the enclosed proxy card intend to vote for all of the nominees named below, unless authority to vote for any or all of the nominees is withheld. In the unanticipated event that any nominee for Director cannot be a candidate at the Annual Meeting, the appointed proxies will vote their proxy in favor of the remainder of the nominees and, in addition, in favor of such substitute nominee(s) (if any) as the Board of Directors shall designate. Alternatively, the proxies may vote in favor of a resolution reducing the number of Directors to be elected at the Annual Meeting.

Information Concerning Nominees

Each of the nominees is listed below. The address of each nominee is Montgomery Street Income Securities, Inc., c/o Jackson Fund Services, 225 West Wacker Drive, Suite 1200, Chicago, Illinois 60606. Each nominee has consented to be nominated and to serve if elected.

The following are some of the experiences, qualifications, attributes and skills of the nominees that led to the conclusion that they should serve as Directors of the Fund:

Mr. Bradshaw has held senior positions in complex enterprises involving venture capital, investment management, legal services, corporate finance, banking, and real estate over his career. He brings to the Board the management experience and insight that he has developed. In addition, Mr. Bradshaw’s 22 years of service on the Board has given him insight into, and perspective on, the Fund’s history and operations, which assists the Board in its oversight of the Fund.

Mr. Hymes has served in chief executive, chief investment, and other senior management roles with investment management firms over the course of his career, including with one of the former investment managers of the Fund. He brings to the Board experience in the field of investment management, which provides the Board with perspective in its oversight of the Fund’s investment activities. His experience with investment products also assists the Board in its oversight of Fund risks. Mr. Hymes’ 8 years of experience on the Board and 2 years as the Fund’s President has given him insight into, and perspective on, the Fund’s history and operations, which assists the Board in its oversight of the Fund.

Mr. Van Auken has served in senior executive roles in venture capital firms over the course of his career and has led investments in a wide range of industries, including e-commerce, information services, and financial services. His experience in corporate finance and in leading investments provides the Board with assistance in its oversight of the Fund’s investment activities. His experience with investment products also assists the Board in its oversight of Fund risks. Mr. Van Auken’s 19 years of experience on the Board has given him insight into, and perspective on, the Fund’s history and operations, which assists the Board in its oversight of the Fund.

Ms. Wallace has developed significant experience in finance during her time in academia where she teaches classes on asset-backed securitization, real estate investment analysis, real estate strategy, and real estate finance. Additionally, she has served as a visiting scholar at the New York Federal Reserve Bank and the San Francisco Federal Reserve Bank, as the president and board member of a national real estate economics association, and as an editorial board member of an academic journal focusing on computational techniques in the pricing, hedging and risk management of financial instruments. Ms. Wallace’s experience in finance and financial analysis assists the Board in the oversight of the Fund’s investment activities and investment risks. In addition, Ms. Wallace’s 2 years of experience on the Board has given her insight into, and perspective on, the Fund’s history and operations, which assists the Board in its oversight of the Fund.

In order for the Fund to take advantage of certain exemptive rules under the 1940 Act, a majority of the Board members must not be interested persons (“Interested Persons”), as defined in the 1940 Act, of the Fund. Directors of the Fund who are not Interested Persons are referred to in this Proxy Statement as “Independent Directors.” If the nominees proposed for election as Directors of the Fund are elected, all the members of the Board of Directors will be Independent Directors. As required, each of the nominees who will be considered an Independent Director, if elected, was selected and nominated solely by the current Independent Directors of the Fund.

Each nominee currently serves as a Board member of one portfolio in the complex of funds that hold themselves out as related companies for purposes of investment or investor services or are managed by the Fund’s investment adviser, Pacific Investment Management Company LLC (“PIMCO”), or its affiliated persons (the “Fund Complex”). PIMCO is located at 840 Newport Center Drive, Newport Beach, California 92660.

As of March 31, 2013, none of the nominees beneficially owned securities of PIMCO or any person directly or indirectly controlling, controlled by or under common control with PIMCO.

Board Leadership Structure

The primary responsibility of the Board of Directors is to represent the interests of the stockholders of the Fund and to provide oversight of the management of the Fund.

The Board is committed to maintaining its independence, and the Board currently is comprised entirely of Independent Directors. It has further been the practice of the Fund to appoint an Independent Director as Chairman of the Board (the “Chairman”) and a separate Chief Executive Officer. The Board believes that an Independent Director can best provide the necessary leadership and objectivity required in a Chairman and that separation of the roles of Chairman and Chief Executive Officer eliminates conflicts of interest that may arise when the roles are combined. It is also noteworthy that the Chief Executive Officer of the Fund is not affiliated with PIMCO, the Fund’s investment adviser, but rather is an officer of the independent Administrator of the Fund.

Board Risk Oversight

As part of its oversight function, the Board supervises the risk management of the Fund. Risks to the Fund include, among others, investment risk, financial reporting risk, and compliance risk. Consistent with New York Stock Exchange requirements, the Board has adopted procedures regarding risk assessment and management that are reviewed annually by the Audit Committee. Under these procedures and in accordance with other Fund practices, the Fund’s officers and service providers are responsible for monitoring and managing the various risks, implementing appropriate policies and procedures, and reporting to the Board and its Committees on a periodic or exceptional basis. For example, the Fund’s investment adviser is primarily responsible for implementing the Fund’s investment program, the Fund’s Administrator is primarily responsible for assuring the Fund’s accounting is appropriately carried out, the Fund’s Chief Compliance Officer is primarily responsible for evaluating the adequacy and effectiveness of the compliance programs of the Fund and its service providers, and the Fund’s independent auditors are primarily responsible for conducting the annual audit of the Fund’s financial statements.  The Board and its Committees are responsible for overseeing the risk-related activities of the Fund’s officers and service providers, reviewing their reports, and taking appropriate action within the scope of their duties under federal and state law. Despite the Board’s oversight, it is likely that not all risks to the Fund will be identified or eliminated.

Board Nominations

The Board of Directors does not have a nominating committee or a charter relating to the nomination of Directors. The full Board considers possible candidates to fill vacancies on the Board of Directors, reviews the qualifications of candidates recommended by stockholders and others, and recommends the slate of nominees to be proposed for election by stockholders at each annual meeting. As noted above, individuals who would be considered Independent Directors, if elected, must be selected and nominated solely by the Independent Directors of the Fund. In light of the fact that all the members of the Board of Directors are Independent Directors, the Board believes that it is appropriate for the full Board to participate in the consideration of Director candidates.

The Board considers diversity in identifying nominees for Director and in evaluating periodically the composition of the Board as a whole. The Board believes that diversity with respect to viewpoint, skills and experience should be an important factor in Board composition. The Board does not have any written policy with regard to the consideration of diversity.

Stockholders wishing to recommend any Director candidate should submit in writing a brief description of the candidate’s business experience and other information relevant to the candidate’s qualifications to serve as a Director. Submissions should be addressed to the Chairman of the Board of Directors, Montgomery Street Income Securities, Inc., c/o Jackson Fund Services, 225 West Wacker Drive, Suite 1200, Chicago, Illinois 60606. In order to be considered at the 2014 Annual Meeting of Stockholders (the “2014 Annual Meeting”), submission must be received by January 21, 2014.

Communications with the Board

The Board of Directors provides a process for stockholders to send communications to the Board. Correspondence should be sent by U.S. mail or courier service to the Chairman of the Board of Directors, Montgomery Street Income Securities, Inc., c/o Jackson Fund Services, 225 West Wacker Drive, Suite 1200, Chicago, Illinois 60606. It is the general policy of the Fund that the Board of Directors should be represented at the Annual Meeting. All of the Directors attended the last Annual Meeting, which was held on July 17, 2012.

Board Committees; Meetings

The Board of Directors has an Executive Committee, a Valuation Committee and an Audit Committee. In 2012, the Board of Directors held five meetings, the Valuation Committee held one meeting, the Audit Committee held two meetings, and the Executive Committee did not meet. Each Director attended at least 75% of the total number of meetings of the Board of Directors and of the Committees of the Board on which he or she served in 2012.

Executive Committee

The Executive Committee is authorized to exercise all powers of the Board of Directors permitted to be exercised under the Maryland General Corporation Law. The Executive Committee is composed of two Independent Directors: Messrs. Bradshaw and Hymes.

Valuation Committee

The Valuation Committee reviews the procedures for the pricing of the Fund’s portfolio assets adopted by the full Board of Directors (the “Pricing Procedures”), assists the Fund’s Administrator in determining the fair value of portfolio assets of the Fund as needed in accordance with the Pricing Procedures, and performs such other tasks as the full Board of Directors deems necessary. The Valuation Committee is composed of three Independent Directors: Messrs. Hymes (Chair) and Van Auken and Ms. Wallace.

Audit Committee

The Audit Committee oversees the accounting and financial reporting policies and practices of the Fund, its internal controls over financial reporting and, as the Audit Committee deems appropriate, the internal controls of certain service providers to the Fund. The Audit Committee also oversees the quality, objectivity and integrity of the Fund’s financial statements and the independent audit thereof; exercises direct responsibility for the appointment, compensation, retention and oversight of the work performed by the independent auditor; reviews the independent auditor’s qualifications and independence; and acts as a liaison between the Fund’s independent auditor and the full Board of Directors.

The Audit Committee is composed of three Independent Directors: Messrs. Van Auken (Chair) and Hymes and Ms. Wallace. Each Audit Committee member meets the independence requirements of the New York Stock Exchange listing standards. The Audit Committee is governed by a written charter adopted by the Board of Directors that sets forth in greater detail the Audit Committee’s purposes, duties and powers. A copy of the current Audit Committee Charter is available on the Fund’s website at www.montgomerystreetincome.com.