"It gives us great satisfaction to see a business we have owned for many years become part of a new powerhouse in the sector as it approaches its centennial year, reinforcing its prospects for even greater success in the future," John Elkann, chairman and chief executive of Exor, said in the statement.

A combination of New York-based Cushman and DTZ will result in a global company to rival CBRE Group and JLL, the industry's No1 and No2 firms, respectively. Creating a brokerage of that heft has been a goal for Brett White, executive chairman of DTZ and CBRE's former chief executive.

The joint company would have more than US$5.5 billion in annual revenue and more than 43,000 employees, Cushman said in a separate statement.

Exor said the deal represents a capital gain of about US$722 million for its stake in Cushman. The transaction is expected to close in the fourth quarter.

TPG, based in Fort Worth, Texas, is a global private investment firm founded in 1992, with more than US$67 billion of assets under management. It bought DTZ late last year.

In January, DTZ completed the acquisition of Cassidy Turley, a brokerage with strength in the Americas, creating a global top-three commercial real estate services firm.

The combined company has about US$2.9 billion in annual revenue, according to a statement at the time.

DTZ had a market share for commercial property sales of more than 50 per cent in China and was ranked third in that category in Britain, according to the January statement.

Cushman reported revenue of US$2.85 billion last year.

Net income rose 33 per cent to US$61.6 million from the previous year.

Fee and service revenue from the Asia-Pacific region climbed 25 per cent.

Founded in 1917, the company has 259 offices in 60 countries, employing more than 16,000 professionals.