Hentons, which operates a team of more than 80 staff across offices in Leeds and Sheffield, said the merger will support its expansion in North and East Yorkshire.
The deal, for an undisclosed sum, will see the York team expanded.
Forster Stott & Co has a heritage in York and Thirsk going back 110 years. A spokesperson said its team will be retained and expanded.
Nadeem Ahmed, managing partner of Hentons said: “Our partner-led entrepreneurial approach has supported the rapid growth of Hentons over the last couple of years.
“Business owners value the wide range of services they can access through our partners.
“We are now undertaking a period of expansion through organic growth and acquisition that will see us servicing a bigger footprint in the North.”
Steve Kilmartin, managing partner of Forster Stott & Co, said: “Both companies share a focus on providing an excellent partner-led service to clients.
“Hentons has made a tremendous investment in technology, and our clients will benefit enormously from the new digital platforms.
“It is good news for our clients, who can now also access advisory services ranging from expert tax advice to wealth management and corporate finance.”
Lloyds Bank Commercial Banking has provided Hentons with a multi-million pound funding package to support the deal.