SJ Berwin managing partner Ralph Cohen is to stand down from the role in the autumn, 18 months before the end of his term was due to end.
Cohen, who has been in the position since 2002, said he had “been thinking about it for some time” and would return to his EU and competition practice at the end of a short handover period.
The City firm is currently in merger talks with US firm Proskauer Rose, with a deal understood to be in the offing later this year.
Cohen said: “If the merger goes ahead I’ve decided it might need new management from our side of things. It’s time for a change after a significant period of time.”
Cohen’s second term as managing partner – the first in the firm’s history – was due to come to an end in 2012, at the same time as senior partner Jonathan Blake’s. Cohen said that the decision was in part due to wanting to avoid the possibility of two sets of elections simultaneously.
He added: “There’s never a perfect time [to do it] and with the loss of a managing partner or senior partner there are always reasons you shouldn’t do it, but this felt like the right time.”
A decision on the election process at the firm will be taken in September, with the election itself held shortly after.
The announcement comes after SJ Berwin experienced a troubled recession. Turnover at the firm dropped by around 20 per cent between 2007-08 and 2009-10, from £215m to £171m. During the same period average profit per equity partner (PEP) fell from £801,000 to £447,000, representing a decline of 44 per cent.