He played college hockey for the Harvard Crimson from 1970 to 1973 and played for the United States at the 1973 World Championship. The Boston Bruins chose him 56th oevrall in the 1971 NHL Amateur Draft. Hynes turned pro with the Bruins and the Boston Braves in 1973-74. In two seasons he played in 22 NHL games and scored 4 goals. After playing for the Rochester Americans in 1974-75 and 1975-76 Hynes tried his luck in the World Hockey Association. Hynes retired in 1978 after playing a year for the Springfield Indians.