The merger of employee benefits consultancy firms Watson Wyatt and Towers Perrin has been completed to form global professional services company Towers Watson.

Watson Wyatt's chief executive John Haley will serve as Towers Watson’s chairman and chief executive and Towers Perrin's CEO Mark Mactas will serve as deputy chairman, president and chief operating officer.

Haley said: “We are delighted to finalise the merger and look forward to bringing a broader portfolio of services to our clients. When it comes to managing costs, risks and people, the world is growing more complex every day. Towers Watson is uniquely positioned to help our clients gain the perspective necessary to take the right actions to drive business results."

Based on the closing price of Watson Wyatt common stock on December 31 2009, the estimated value of the transaction is $4 billion.