Graduated from the high school.
Born in Maine, Mullen served as the farm system director and head of minor league operations with the Milwaukee/Atlanta Braves from 1960 to 1966. In 1967, Mullen became the executive assistant to the general manager of the Houston Astros. He served as acting general manager from July 10 to August 7, 1975, when Tal Smith assumed the permanent GM role.
He remained with Houston until 1979. Mullen then returned to the Braves as their general manager in May 1979 after the sudden death of Bill Lucas. After being replaced by Bobby Cox in 1986, Mullen served as vice president and assistant general manager of the Braves until 1990.
John Mullen died at age 66 in West Palm Beach, Florida, on Wednesday, April 3, 1991, having been found dead in his hotel room that morning. Said Cox upon Mullen's death, "John had been with the Braves since their Boston days. No one has done more for the Braves than John Mullen.
We'll all miss him.".
Served with United States Coast Guard, 1942-1946.
Married Claire Elaine Babineau, May 4, 1946. Children: Kathleen C., Christopher J., Richard A.