Alistair Macdonald (left), CEO of INC Research, will serve as CEO of the newly combined company. Michael Bell (right), CEO of inVentiv Health, will act as executive chairman.

Contract research organization INC Research said Wednesday it plans to acquire inVentiv Health in a deal worth $4.6 billion. 

The deal will create one of the three biggest contract research organizations in the world.

This tie-up was announced one year after inVentiv had filed an IPO, which it cancelled it after receiving investment from private equity company Advent International. Advent valued inVentiv at $3.8 billion at the time. That deal made Advent an equal owner with Thomas H. Lee Partners, another private-equity firm that acquired inVentiv for $1.1 billion in 2010. Advent and Thomas H. Lee Partners will own 47% of the new company if the deal closes.

INC will own 53% of the newly combined company, whose name has yet to be determined.

See also: InVentiv Health files for IPO

InVentiv Health owns nine healthcare advertising and marketing agencies in North America: Addison Whitney, Biosector 2, Chamberlain Healthcare Public Relations, Chandler Chicco Agency, GSW, inVentiv Health Managed Markets, inVentiv Health Medical Communications, Navicor Group, and PALIO. The company acquired two CROs, PharmaNet Development Group and Kforce Clinical Research, in 2011 and 2012, respectively.

INC is a CRO based in Raleigh, North Carolina that helps drugmakers conduct clinical trials of investigational drugs.

“Through this strategic combination we are bringing together two of the most innovative and respected players in the field to create a leading global biopharma solutions organization,” Alistair MacDonald, CEO of INC Research, said in a news release.

See also: Palio consolidates, closes two offices

The combined company will employ roughly 22,000 people. It will be headquartered in Raleigh, North Carolina. It will also pair two companies with differing client bases; INC traditionally serves more small to mid-size clients, while inVentiv counts more large pharma clients on its roster.

Andrew Macdonald will serve as CEO of the new company; Greg Rush, CFO of INC Research, will serve as the company’s new CFO; and Michael Bell, chairman and CEO of inVentiv Health, will serve as executive chairman of the new company.

Another major CRO, Quintiles, was acquired by IMS Health in a $9 billion deal last year.