The French arm of US firm Jones Day is drawing up plans to move into the Hôtel de Talleyrand, formally the US government's state apartments in Paris.
The move will boost the 90-lawyer firm's office space by 40 per cent, providing room for around 130 lawyers.
Following 9/11, the US Department of State's Overseas Buildings Operations (OBO) audited all its buildings for security in the event of a terrorist attack.
It found the Talleyrand a security risk as it backs onto the Rue de Rivoli, a main thoroughfare in Paris, and so ordered the space to be let to a commercial tenant.
Jones Day France managing partner Wesley Johnson said: "It's an absolute gem: a witness to two centuries of European and world history.
"It will be unique, but also very practical for a law practice."
Under the terms of the agreement Jones Day will be responsible for converting the Talleyrand into commercial office space. Unusually for an office move, Jones Day had to go through a tender process before winning the space.
The building work is due to be finished next year, with the firm opening its gilt-edged doors in the autumn of 2008.