He will remain with the company until Dec. 31, 2012 and serve as a consultant to Willis through 2013. Willis says his consulting support will “ensure a smooth transition.”

While he remains employed by Willis in 2012, Millwater “will resign from all directorships and other positions that he holds with Willis and its subsidiaries with effect at the end of the day” on Dec. 31 of this year, according to a filing with the Securities and Exchange Commission.

In his position as a consultant, Millwater will receive a consulting fee of £75,000 ($117,536) a month. His consulting services are exclusive to Willis, but he will be allowed to pursue other business interests outside of working for other major brokerage firms.

“My partnership, and friendship, with Grahame began upon my arrival to Willis in 2000 and continues to this day,” says Joe Plumeri, chairman and CEO of Willis in a statement. He added that he has tremendous gratitude for Millwater's 26 years of service.

“After spending my entire professional career since leaving university with one company, I have been privileged to work with an extraordinary team of people from around the world and am retiring from Willis with many friends,” says Millwater in the same statement. He says he looks forward to spending time with his family and “considering new opportunities.”

As a result of the change, Willis says that Steve Hearn, CEO of Willis Re will also serve as chairman and CEO of Willis Global. Tim Wright, CEO of Willis International, will oversee Willis U.K. and Ireland.