Yorkshire's Keeble Hawson has merged with Frank Allen Pennington, giving the firm a new base in Doncaster.
Keeble senior partner Tony Gregory said: "We think that Doncaster's very much an up-and-coming area and is undervalued and under-served by the legal profession."
The merger gives Keeble 30 new lawyers, including Frank Allen Pennington senior partner Paul Pennington and three other partners.
Only three of these will become partners at the new firm, bringing the merged firm's total partnership to 29 members.
Frank Allen Pennington's other two partners, one who practises criminal law and one dispute resolution, will not join the new firm.
Pennington said: "Merging with Keeble Hawson for the first time creates a firm in the town which can advise companies from the early stages of start-up right through to flotation on the investment markets.
"All too often we see this business leaving Doncaster for Leeds or Manchester."