City firm Vizards Staples & Bannisters has taken the pensions practice from rival London firm Howard Kennedy.
Head of pensions Graham Chrystie and his assistant are moving their department and all their clients to Vizards Staples.
Chrystie acted in the longest running pensions litigation in history when he represented members of pension schemes run by packaging giant Melton Medes in a dispute over management.
He also advises the South African government on pensions legislation.
Chrystie says he is moving because Howard Kennedy has decided to concentrate on property work.
"Howard Kennedy has shut down everything to do with pensions and everything has come across.
"It's focusing much more on its traditional strength of property."
Chrystie will be the first partner at Vizards Staples specialising in pensions.
Senior partner Martin Staples says: "He will be a huge boost to our business services group. There is a huge amount of work available in that area and there will be more with the new employment legislation."
Howard Kennedy senior partner Trevor Newey says the firm will continue to develop areas other than property. He refused to comment on whether the firm plans to replace Chrystie.