North America chief Nick Cowling said the firm wanted to expand its leadership team amid strong growth in the region.
Friedman, who left Ogilvy late last year, is based in New York and oversees client service, talent management and business development for the US market. He spent 16 years at Ogilvy & Mather and Ogilvy PR, including as managing director for Chicago and regional managing director of its four West Coast offices. He also led the Americas for the WPP group handling LG Electronics.
Citizen Relations, based in Los Angeles, was acquired by China's BlueFocus Communications in 2014. It has nine offices and a client roster than spans Aflac, Travelocity and P&G Brands.
The agency, the former Citizen Paine, was forged in 2011 by PainePR (US), Optimum (Canada), Band & Brown and Brando (UK).