HVA, Greenland Houchen Pomeroy (GHP) and Overbury Steward & Eaton (Overburys) will rebrand as Spire Solicitors to increase its presence in Norfolk and specialise more in social housing, commercial property and agriculture.
Jeremy Whigam, partner at HVA, who will retire following the merger to the role of consultant, said the merger had been in the making for eight months and was a response to the threat from Tesco law and London competition.
He said: "When we had further discussion with GHP about potentially merging it occurred to us that with Overburys we would all be a good fit together.
"In terms of regional coverage it works well because all our firms are in and around Norwich. For market-town practices unless there is specialisation or size the days are numbered because of increasing competition. Recruitment is also difficult in small cities such as Norwich."
Alisdair Liddle, partner at Overburys, added the merger was a response to the changes in the legal services market and future rising challenges.
Spire's head office will be in Norwich with seven market town offices in Attleborough, Aylsham, Dereham, Diss, Long Stratton, Watton and Wymondham. Merger completion is expected on 1 August 2013.
The firm will register as an alternative business structure to allow external investment.