CGNU chief executive Bob Scott is to step down at the group's annual meeting in April, by which time he will have been steering CGU's £18bn merger with Norwich Union for almost a full year.
His nominated successor is Richard Harvey, currently CGNU deputy chief executive, who takes over on April 24 when Scott retires.
Harvey, 50, joined Norwich Union in New Zealand in 1992, and has held various high level positions with the insurer, including group finance director and chief executive.
Commenting on the change, CGNU chairman Pehr Gyllenhammar, said: “The integration has progressed well and it is timely for us to shape the executive team which, under Harvey's leadership, can take CGNU on to the next stage in its development.”
Scott has overseen the merger of three insurance groups since he became group chief executive of General Accident in 1996.
He was the first chief executive of CGU when GA merged with Commercial Union in 1998.
He stepped into the role of chief executive of CGNU in May 2000, when CGU amalgamated with Norwich Union.
Also joining the board of CGNU is Mike Biggs, currently executive director responsible for UK general insurance. He replaces Peter Foster as group finance director from March 31.
And Patrick Snowball is promoted from managing director to group executive director for UK general insurance on March 31.
Lyndon Bolton, a non-executive director of CGNU, also retires at the group's AGM. He was a former non-executive director of GA.