Stephen Gilmore is stepping down as head of law firm, Cobbetts, in Birmingham.
The move comes two years after he steered the then Lee Crowder into a merger with its northern rival, which has proved largely successful.
He will stay on as a consultant but says he wants to switch out of the profession and into mainstream business. He is succeeded as partner in charge of the Birmingham office by Graham Muth.
A corporate specialist, Mr Muth began his legal career in 1981 when he joined Lee Crowder as a trainee and quickly rose through the ranks, becoming a partner in 1987.
He sat on the firm's executive board and played an instrumental role in the 2004 Cobbetts deal.
In his consultancy role, Mr Gilmore - thirty years at Lee Crowder/Cobbetts - will assist with a number of the firm's key client relationships, while also developing his other business interests.
He became senior partner at Lee Crowder in 1995 when it was a firm turning over just £2 million. He shaped its development, taking it through to its eventual merger with Cobbetts. Since the merger, he has assisted with Cobbetts' continued growth, helping it to achieve top 50 status and increasing turnover to £58 million.
Michael Shaw, Cobbetts' managing partner, said: "Stephen has been pivotal in the development of first Lee Crowder and then Cobbetts' Birmingham office over the past 11 years.
"During his time in charge, he has been the architect of the rapid growth of the office. We are pleased to be continuing our relationship with him in his new consultancy role and will wholeheartedly support him with his other business activities.
"I am delighted Graham is taking on this important role within Cobbetts. He brings with him an excellent reputation in the marketplace and the commitment and enthusiasm to continue our growth in Birmingham."
Mr Gilmore said: "I am proud of what has been achieved in Birmingham, which has been possible only with the support of exceptionally talented people throughout the firm.
"It has been a privilege to have been involved in developing such a great business. However, I have always considered myself a businessman who happens to be a lawyer and the time has come to explore other opportunities."