
<PAGE>   1
                                                                    EXHIBIT 5.1


        [CHAMBERLAIN, HRDLICKA, WHITE, WILLIAMS & MARTIN LETTERHEAD]





                               September 11, 1995




Stewart Information Services Corporation
1980 Post Oak Boulevard
Houston, Texas 77056

Gentlemen:

         We have acted as your counsel in the preparation and filing of a
Registration Statement on Form S-8 under the Securities Act of 1933, as
amended, relating to the registration of (i) participa-tions in the Stewart
Title Guaranty Company Salary Deferral Plan and Trust (the "Plan") and (ii)
shares of Common Stock of Stewart Information Securities Corporation (the
"Company"), both of which may be offered under and pursuant to the Plan.

         You have requested that we furnish you this legal opinion concerning
certain matters about the Company, the Plan and the securities being
registered.  In connection with this opinion, we have examined originals, or
copies certified or otherwise identified to our satisfaction, of such
documents, corporate records, and other instruments and have made such other
and further investigations as we have deemed necessary to enable us to express
the opinions hereinafter set forth.

         Based upon the foregoing, we are of the opinion that:

         1.      The Company was duly and validly organized and is validly
existing in good standing as a corporation under the laws of the State of
Delaware.

         2.      The Plan constitutes a valid and legally binding agreement of
Stewart Title Guaranty Company conferring valid, legal interests in the Plan in
eligible employees participating therein to the extent and upon the terms and
conditions described therein, and when issued pursuant to the terms and
conditions of the Plan, such interests will be legally issued, fully paid and
nonassessable.
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Stewart Information Services Corporation
September 11, 1995
Page 2




         The foregoing opinion concerning the legality, validity, binding
nature and enforceability of the Plan, is subject to the general principles of
equity (regardless of whether such question is considered in a proceeding in
equity or at law), and to applicable bankruptcy, insolvency, moratorium,
fraudulent or preferential conveyance and other similar laws affecting the
enforcement of creditors' rights.

         This opinion is solely for your benefit, and may not be relied on by
any person other than you and your counsel.

         This opinion is rendered as of the date hereof and we undertake no,
and hereby disclaim any, obligation to advise you of any changes in or new
developments which might affect any matters or opinions set forth herein.

         We hereby consent to the filing of this opinion as an Exhibit to the
Registration Statement on Form S-8.

                                            Very truly yours,
                                           
                                            CHAMBERLAIN, HRDLICKA, WHITE
                                              WILLIAMS & MARTIN
                                           
                                           
                                           
                                            /s/ Stephen M. Mason
