In 1965, he managed the Athletics for 136 games, finishing with a 54-82 record. At the end of that season, he joined the Red Sox as director of player personnel.
Sullivan, Jean Yawkey and Buddy LeRoux became owners of the Red Sox in 1978 and Sullivan became the team's general manager. He held the job until 1983. One of his more infamous moments came when he forgot to mail a contract offer to Carlton Fisk. The oversight allowed Fisk to become a free agent and sign with the White Sox in 1981.
On June 6, 1983, LeRoux made the announcement -- during Tony Conigliaro Night -- that he had taken over the team from Sullivan and Yawkey. Part of the announcement was that he and two other co-owners had reorganized the team and made LeRoux a general partner.
LeRoux's first act of business was to terminate Sullivan and hire Dick O'Connell as general manager. The move resulted in a court case and Sullivan finished out the season as the general manager. He last worked for Boston in 1993. Following his career with the Red Sox, Sullivan ran a marina in Fort Myers. His son, Marc, was a major league catcher from 1982-87