Manchester firm Slater Heelis - which can trace its roots back over 225 years - is to break up.
Highly rated senior partner Egan Brooks and six other partners are joining Addleshaw Booth & Co. A further nine partners, including the firm's head of corporate Christopher Dunn and head of litigation Kevin Jaquiss, are going to Cobbetts.
The firm's three-partner Sale office - which does mainly private client and conveyancing work - is to set up on its own as Slater Heelis Sale.
The firm, set to close in November, insists its break-up is amicable.
Jarath Walsh, the new managing partner of Slater Heelis Sale, said the firm examined a number of options including a merger, before deciding to break up.
A senior partner at a rival firm said: "It wasn't big enough to service its main clients, including NatWest, and wasn't in a position to reinvent itself as a niche practice."
The arrival of Brooks - who is contact partner for NatWest - and his team is a major boost for Addleshaws, which has just opened a five-fee earner London office.
His team is joining the insolvency practice, which was hit by the departure of its head, Shan Spencer, to niche Manchester practice Chaffe Street in April.