The discussions are understood to have taken place with London-based Kennedys.
Kennedys has nine UK offices, although none in Scotland, and nine abroad in locations such as the US, Spain and Australia.
The 33-partner Simpson & Marwick specialises in insurance work and has offices in Edinburgh, Aberdeen, Glasgow, Dundee, North Berwick, Newcastle and London.
A partner at the firm, who asked not to be named, said the discussions were at a very early stage and the next phase would involve speaking to clients.
If clients are supportive of the proposals, further talks on a merger are likely to take place next year.
The partner said: "The firms have known each other for several years.
"We have been having discussions and now we need to speak to clients. Any news of a merger is greatly exaggerated. There are commercial pressures we have to factor in. We may need to get on a bus but it may not be this bus."
The firms are thought to share some common clients keen to have a one-stop service for their needs.
This year insurance-focused Scots firm Andersons merged with DAC Beachcroft. There have been a number of other cross-border mergers in 2012 including McGrigors with Pinsent Masons, Archibald Campbell & Harley with Shoosmiths, and DWF with Biggart Baillie.