Exhibit 10.1

EXECUTION VERSION

AMENDMENT NO. 1 TO VOTING AGREEMENT

This AMENDMENT NO. 1 TO VOTING AGREEMENT, dated as of November 19, 2015 (this
“Amendment”), is by and among Towers Watson & Co., a Delaware corporation (the
“Company”) and the shareholders of Willis Group Holdings plc, an Irish public
limited company (“Parent”) listed on Schedule A thereto (each, a “Shareholder”
and, collectively, the “Shareholders”).

WHEREAS, the Company and the Shareholders entered into that certain Voting
Agreement dated as of June 29, 2015 (the “Voting Agreement”);

WHEREAS, Section 11 of the Voting Agreement provides that the Voting Agreement
may be amended, modified and supplemented by written agreement of the parties;

WHEREAS, the Company and the Shareholders now intend to amend certain provisions
of the Voting Agreement as set forth herein.

NOW, THEREFORE, in consideration of the mutual covenants and agreements
contained in this Amendment and for other good and valuable consideration, the
receipt and adequacy of which are hereby acknowledged, the Company and the
Shareholders agree as follows:

1. The term “Merger Agreement” as used in the Voting Agreement means the
Agreement and Plan of Merger by and among Willis Group Holdings Public Limited
Company, an Irish public limited company (“Parent”), Citadel Merger Sub, Inc., a
Delaware corporation and wholly-owned subsidiary of Parent, and the Company
dated as of June 29, 2015, as amended by Amendment No. 1 to Agreement and Plan
of Merger, dated as of November 19, 2015.

2. Each Shareholder, as to itself (severally and not jointly), hereby represents
and warrants to the Company as follows: this Amendment has been duly and validly
executed and delivered by each Shareholder and, assuming due authorization,
execution and delivery by the Company, constitutes a legal, valid and binding
obligation of such Shareholder, enforceable against such Shareholder in
accordance with its terms, except as enforcement may be limited by applicable
bankruptcy, insolvency, reorganization, moratorium or similar laws affecting
creditors’ rights generally and by general principles of equity (regardless of
whether considered in a proceeding in equity or at law).

3. Other than as specifically set forth herein, all other terms and provisions
of the Voting Agreement shall remain unaffected by the terms of this Amendment,
and shall continue in full force and effect.

4. This Amendment may be executed in two or more counterparts, all of which
shall be considered one and the same instrument and shall become effective when
one or more counterparts have been signed by each of the parties and delivered
to the other party.

5. This Amendment may be executed by facsimile or .pdf signature and a facsimile
or .pdf signature shall constitute an original for all purposes.

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IN WITNESS WHEREOF, the Company and the Shareholders have caused to be executed
or executed this Amendment as of the date first written above.

 

TOWERS WATSON & CO. By:  

/s/ John H. Haley

  Name:    John J. Haley   Title:      Chief Executive Officer VALUEACT CAPITAL
MASTER FUND, L.P. By: VA Partners I, LLC, its General Partner By:  

/s/ Bradley E. Singer

  Name:    Bradley E. Singer   Title:      Chief Operating Officer VA PARTNERS
I, LLC. By: ValueAct Holdings, L.P., its General Partner By:  

/s/ Bradley E. Singer

  Name:    Bradley E. Singer   Title:      Chief Operating Officer VALUEACT
CAPITAL MANAGEMENT, L.P. By ValueAct Capital Management LLC, its General Partner
By:  

/s/ Bradley E. Singer

  Name:    Bradley E. Singer   Title:      Chief Operating Officer VALUEACT
CAPITAL MANAGEMENT, LLC By: ValueAct Holdings, L.P., its General Partner By:  

/s/ Bradley E. Singer

  Name:    Bradley E. Singer   Title:      Chief Operating Officer

SIGNATURE PAGE TO AMENDMENT NO. 1 TO VOTING AGREEMENT

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VALUEACT HOLDINGS, L.P. By ValueAct Holdings GP, LLC, its General Partner By:  

/s/ Bradley E. Singer

  Name:    Bradley E. Singer   Title:      Chief Operating Officer VALUEACT
HOLDINGS GP, LLC By:  

/s/ Bradley E. Singer

  Name:    Bradley E. Singer   Title:      Chief Operating Officer

SIGNATURE PAGE TO AMENDMENT NO. 1 TO VOTING AGREEMENT