Mr. Hagedorn, 38, previously managing director of the Eastern region for sibling Omnicom media agency OMD USA, will be based in New York. He will report both to Mike Cooper, CEO of PHD Worldwide, and Page Thompson, who was named CEO of Omnicom Media Group North America earlier this week.
'Unique and diverse background'
"Scott has a unique and diverse background, having worked in digital, direct and, more recently, running a large media operation," Mr. Cooper said in a statement. "His experience on major accounts and new-business track record make him the perfect choice to lead PHD USA. He's also a great fit with the PHD culture."
Before joining OMD, Mr. Hagedorn was chief interactive officer for Omnicom direct-marketing firm Rapp Worldwide, leading Rapp's national digital client, creative, analytics and technology teams.
"I'm thrilled to be given the opportunity to lead this progressive firm in the U.S.," Mr. Hagedorn said in a statement. "I look forward to leveraging all that I've learned during my career to advance the agency."
Since July, when Mr. Seiler left PHD USA, the agency has been run by an interim team composed of managing partners Jean Neal, John Swift, Susan Taylor and Fred Foster, along with Mr. Cooper.