Keppie Architects and Seymour Harris Architects have entered into talks that could culminate in a formal merger.
The move would leave the combined company with a staff of more than 200 and a presence in most of the UK's major cities.
If the merger goes ahead it will be the culmination of a successful alliance between the offices, first instigated five years ago to allow the firms to bid for PFI work.
Seymour Harris managing director Tony Clark told the AJ that talks were under way. 'We are in discussion with Keppie and after our successful collaboration it seemed sensible we should talk about merging.'
However, Keppie was more reticent. Business development manager Andrew Pinkerton said a merger wasn't a certainty. 'We are in talks about how to take our collaboration forward, but whether this will lead to a merger I cannot say, ' he said.