Birmingham-based quantity surveyor Francis Graves & Naismiths has been sold to quoted company Erinaceous.
Graves, best known for its work on the NEC and ICC, is part of a string of acquisitions by the Croydon company.
The Entente group - trading as Francis Graves and Naismiths - was picked up for £7 million.
Richard Graves, son of founder Francis Graves, said Erinaceous had initiated an approach with the offer coming "out of the blue".
He said: "They are big in Manchester and London and wanted a Midlands operation on which to build."
FG&N has a turnover of £6.25 million, made £1.4 million profits in the year to June, and employs 85 people.
Mr Graves, who will remain with the firm, said it would be run as an autonomous subsidiary. He said the deal offered employees more security and opportunity.
"It is good news," said Mr Graves. "We are looking forward with optimism."
Erinaceous said the deal added "a range of professional services in the property services sector and expands the group's geographic presence through its principal offices in Birmingham, Leeds and Manchester".
Francis Graves and Naismiths came together in 2003.
Richard Graves brought in Francis Graves and John Johnson took Naismiths to the party as both realised there was a need to get bigger.
Francis Graves provides quantity surveying, project management and consultancy services to the UK property and construction sectors. Naismiths, established in 1963, specialised in the provision of consultancy skills to the construction corporate recovery sector.
Already integrating two previous acquisitions, Hercules and ISG Occupancy, Erinaceous has in addition to Graves picked up Manchester architects Leach Rhodes Walker for £9 million, London lettings agent Ironsides and Manchester building consultancy EP2.
Established for more than 50 years, Leach Rhodes Walker employs around 90 staff and has been involved in major developments such as the Trafford Centre, the new airport at Doncaster, town centre and retail developments, office buildings and projects in the hotel and leisure industries.
Erinaceous, which describes itself as a "one-stop shop" property support services group operating in the public and private sectors, said the first half had seen good progress in integration and consolidation of the various acquisitions.
It announced turnover of £67.6 million up from £38 million in September 2004 including underlying organic growth of seven per cent.
Operating profit was £13.4 million, up from £2.8 million, including underlying organic growth of 26 per cent.
Pretax profit came in at £12.1 million against £2.6 million.
Earnings per share of 9.3p was an increase of 116 per cent. An interim dividend of 2.75p per share has been declared.
Neil Bellis, chief executive, said: "This has been a successful half year. The group has made good progress on its integration programme and achieved a strong set of financial results which provide a sound platform for continued growth."
Following the acquisitions the group now had a presence in ten UK cities. Cost savings of £2 million had been achieved across the group.