Stephen Gilmore, former head of Cobbetts' Birmingham office, has quit to join the Wilkes Partnership.
It is the second major defection this year - in February four partners and their teams from the social housing group switched to Shoosmiths.
It comes as major change has been engulfing the Cobbetts operation, with a remuneration shake-up and partner departures.
But the law firm has been fighting back, looking to raise its profile - for example through sponsoring the recent Birmingham Young Professional of the Year competition.
Mr Gilmore has more than 25 years experience in the Birmingham legal sector. He trained at Lee Crowder & Co where he became senior partner in 1995, at the age of 39.
He was the architect of the firm's move to Birmingham city centre and its rapid expansion, leading to its eventual merger with Cobbetts in 2004. He became partner-in-charge of Cobbetts' Birmingham office before retiring from the role in April 2006.
Mr Gilmore has since held a number of non-executive director and consultancy roles with local businesses including property firm Mucklow, and is chairman of Acorns Children's Hospice.
He will be with Wilkes part-time.
He said: "I am looking forward to working with the Wilkes Partnership to develop all aspects of their business. They are a firm with a long history of commitment to the Birmingham market place, which reflects my own out-look. I am sure that I will enjoy working there."
After stepping down as a Cobbetts partner Mr Gilmore had been on a two year consultancy deal, which expired at the end of last month.
Explaining the rationale behind that, he went on: "I decided to make an alteration in my life.
"I had hit 50, we had done the merger and it seemed to be settling down reasonably well, and I wanted to do other things. I wanted a much more varied career."
He intends to maintain a portfolio of interests.
Wilkes Partnership senior partner Nigel Wood said: "We are very pleased that Stephen is joining us. Wilkes is a fiercely independent provider of legal services to the owner managed business and small plc sector. Stephen's experience will enable us to consolidate our position in this market."
Cobbetts' social housing group loss saw a 31-strong team make the move to Shoosmiths, led by partner Andy Ballard. The switch was billed as amicable, but legal sources in Birmingham claimed Cobbetts did not want to lose its people. In January Cobbetts announced a major partner shake-up in a bid to incentivise its lawyers in a new world of competition.
The shake-up came on the back of Cobbetts trimming partner numbers in a bid to become more efficient. Around 20 went in 2006.
Cobbetts saw the introduction of variable equity partner (VEP) and assured equity partner (AEP) status - the former to be paid purely on the profitability of the business while the latter have 90 per cent of their earnings guaranteed with the remaining 10 per cent profit-related. In 2007 Cobbetts reported turnover of £58.5 million and profit per equity partner - there were 30 at that time - of £240,000, up from £190,000.