The deal will create Shakespeare Martineau, employing 900 people with a combined annual turnover of £75 million.
The combined firm will have offices across the Midlands, in Milton Keynes and in London and Brussels.
Each firm currently specialises in distinct sectors and, combined, will strengthen their offering of a compelling service for existing and prospective clients, said Shakespeares chief executive Andy Raynor.
He added: “I am delighted with the way this has gone – all our people have worked together brilliantly.
“Shakespeare Martineau will have a strong commercial personality and the merger demonstrates the commitment of both firms to grow and keep ahead of a rapidly changing and vibrant marketplace.”
SGH Martineau managing partner Emma Shipp said: “Announcing the firm’s merger plans has cemented our shared vision – to be a progressive and distinctive law firm focused on making a difference for our clients.
“I am confident that by joining forces we will have an exciting business in which all of our people can develop and thrive.”
Pictured: Andy Raynor and Emma Shipp.