The new firm – to be named SGH Martineau – will have more than 200 fee-earners and a turnover in excess of £30 million.
Bill Barker, managing partner at Martineau will continue in this role for the new firm, with Andrew Whitehead as senior partner.
SGH managing partner Emma Shipp and head of litigation, David Bailey, will join the executive board to ensure the smooth integration of the two businesses.
Speaking on the merger, Emma Shipp said the two businesses were ‘very similar’ in their outlook and ambitions, which will help as they embark on the process to merge.
She added: "I’m sure this merger offers even greater opportunities for us both and Bill and I share excitement in anticipating the coming months and years.
"This merger will add even greater depth to the high quality service both firms already provide and offer real benefits to clients."
Barker added: "Martineau and SGH are a complementary fit, sharing the same vision and commitment to excellent client service and as Emma said, we’re looking forward to seeing what the future will bring.
"We’re confident that both existing and new clients will be able to take full advantage of the new capabilities offered by SGH Martineau LLP."
By Joe McGrath