Keystone Law is moving into the Northern Ireland market via a merger with Belfast law firm McMahon McKay.

The tie-up will go live on 6 March, with the merged businesses to be called Keystone Law Northern Ireland.

It will operate from McMahon's current location on Adelaide Street in Belfast. John McMahon and Danny McKay, who founded the firm last year, will continue to own and control the business. The firm, which also has one consultant and two trainees, concluded deals with a total value of £400m between April and December last year.

Keystone managing partner James Knight said: "We have been looking to establish operations in Ireland for over two years now, but it has not been easy to find the perfect firm to partner with. The dynamic performance and impressive growth displayed by McMahon McKay caught our attention last year and our discussions have proceeded reassuringly quickly to where they are today."

McMahon – who spent seven years at Belfast firm Johnsons Solicitors before launching McMahon McKay – added: "We totally exceeded our expectations in 2016. This merger will enable us to respond more readily to the increasing client demand and simultaneously grow the business."

Keystone Law Northern Ireland will be supported by the firm's London office, which will provide finance, banking, marketing, IT and general administrative assistance.

Keystone's flexible operating model uses technology to allow many of its 230-lawyers to work from their own offices or homes, though it does have office space in London, Bristol, the Isle of Man, Guernsey, Melbourne and Sydney.

It was founded by Knight in 2002 and is now a full-service law firm with 230 senior lawyers. Its turnover for the 2016-17 financial year was £26m. Keystone's financial year runs from 1 February to 31 January.

The merger comes after Keystone last year made the eye-catching hire of Jonathan Brenner, co-founder of Berwin Leighton Paisner's contract lawyer spin-off LOD.

Brenner splits his time between LOD and Keystone, continuing to work two days each week heading the law firm engagement team at LOD, with the rest of the week spent working for Keystone. He is expected to help Keystone expand its UK headcount and build operations in continental Europe and Asia.