CB Richard Ellis is offering $415m (£259m) for Insignia Financial Group.
Hundreds of jobs are at risk in the UK from what is the biggest property agency takeover to date.
The combined group will have global revenues of more than $1.9bn, more than twice that of Jones Lang LaSalle, the next largest property advisory firm.
The deal reunites Richard Ellis, whose UK and international operations were separated in a deal in 1998.
Ray Wirta, chief executive of CB Richard Ellis and Brett White, president, will lead the combined company. Andrew Farkas, who founded Insignia, will leave and he is expected to start another property business.
References: The Times 19/02/03 page 24 (Need to know), page 27
