Dumaine began working for his father as an errand boy and eventually became the #2 man in his business empire. Following the elder Dumaine's death in 1951, Frederic succeeded his father as president of the
New York, New Haven and Hartford Railroad and the
Amoskeag Company. In 1954, Patrick B. McGinnis won a
proxy fight for control of the New Haven and succeed Dumaine as president. In 1956, Dumaine was part of a group of Boston businessmen who purchased Avis Rent a Car System. He served as the company's treasurer until 1957, when he was elevated to the role of president. In 1962, Amoskeag sold control of Avis to
Lazard Freres and
Robert Townsend succeeded Dumaine as the head of the company. In 1966, Dumaine was elected chairman of the Delaware & Hudson Company; the parent company of the
Delaware and Hudson Railroad. Seven months later he was also given the position of president and chief executive officer. He resigned the following year prior to a vote on a merger with the
Norfolk and Western Railway, which a majority of the D&H board supported, but Dumaine opposed. Dumaine also served as an executive with the
American Woolen Company,
Lehigh Coal and Navigation Company,
Waltham Watch Company,
Fanny Farmer,
Boston Edison Company,
Bangor and Aroostook Railroad,
Pittsburg and Shawmut Railroad,
Boston and Maine Railroad,
Boston Garden-Arena Corporation, and
Springfield and Eastern Street Railway. ==Politics==