The two firms announced earlier this week that Thomas Eggar would be rebranding its offices as Irwin Mitchell by the midpoint of next year.
Irwin Mitchell, based in London, has more than 80 real estate lawyers across 11 UK offices, and lists five people with planning as a speciality on its website.
Thomas Eggar has a similar number of property lawyers, including 20 real estate partners.
Irwin Mitchel was ranked 17th in this year’s Planning Law Survey’s highest rated law firms list. Thomas Eggar was ranked 45th.
No relocations or redundancies are expected in either business.
Irwin Mitchell national head of real estate Paul Firth said: "This merger is very exciting – increasing the size of our real estate business by 80 per cent, giving us even stronger UK coverage and broadening our offer for our real estate clients."
Thomas Eggar managing partner Vicky Brackett added: "Clients of both firms will benefit from a broader range of property expertise, particularly in areas such as planning and construction, and whether acting for a landlord, tenant or funder, our combined strength in numbers will deliver clients a service that is second to none."