He replaces Bob Kuperman, who was the president and chief executive until he retired in January. Kuperman remains as a consultant.
Lee Garfinkel, the chairman of DDB New York, said: "Peter is the perfect partner to help me chart the course for this agency. In this complex environment and ever-changing industry, I am happy to have a leader of DDB New York who has the skills and experience to broaden the platform for the creative solutions we provide."
During his career, Hempel has been the managing director of DDB, the vice-president of global marketing at The Gap and the general manager of Lowe in New York.