Bluefin Corporate Consulting and Capita Hartshead will operate as a combined organisation under the new name Capita Employee Benefits from November 2012.
This follows the acquisition of Bluefin Corporate Consulting by Capita in April 2012.
The combined organisation will offer a range of services, including pension administration and consulting, investment and actuarial consulting, and the design and implementation of health, risk and flexible benefits.
The new business will employ 2,400 people in London, Sheffield and 22 other locations across Britain and Ireland.
Nick Burns, chief executive of the combined business, said: “The merger creates a well-rounded full-service organisation.
“We have big plans for the business, and believe we will be well placed to address the needs of employers in this constantly changing market.”