Davis Langdon has been bought by US engineering giant AECOM for £204m.
Staff were told the news this morning after partners from the construction consultancy's Europe, Middle East and Africa arm approved the takeover.
However, it is thought that the Asian arm of the business, known as Davis Langdon and Seah International, will remain independent but work with AECOM in a collaboration arrangement.
The deal ends months of speculation about Davis Langdon, with another US engineer, Jacobs, also linked with a bid for the firm.
AECOM, which has its head office in Los Angeles, employs 45,000 people globally, and generated annual revenues of £4bn for the year ending 31 March 2010. Its name is an acronym standing for Architecture, Engineering, Consulting, Operations and Management.
Davis Langdon has over 2,750 staff in 75 offices throughout Africa, Australia and New Zealand, Europe, the Middle East, and the USA, and turned over £270m in 2009. Davis Langdon Seah employs 2,000 people in 32 offices in 11 countries across Asia. The combined global business has revenues of £580m.