Born in New York, New York, Jennings was owner of the New York Rangers from 1959 until his death in 1981. The William M. Jennings Trophy was named in his honour. Jennings also helped initiate the Lester Patrick Trophy in 1966, which he would win in 1971. He was elected to the Hockey Hall of Fame in 1975, and the United States Hockey Hall of Fame in 1981.