After fighting in World War II in the U.S. Navy, he returned to the Giants as team vice president, a post he retained after his father died in 1958.

Mara didn't relinquish full control over the football side of the operation until 1979, when George Young became the team's general manager.

The Giants were hamstrung for several years by a strained relationship between Wellington and his nephew Tim J. Mara, who inherited Jack's stake in the team.

The Maras continued to retain close control over the Giants' day-to-day operations long after most other owners had delegated such authority.

When Lawrence Taylor was inducted into the Pro Football Hall of Fame in 1999 he credited Mara for supporting him even during the worst times of his drug addiction saying, "He probably cared more about me as a person than he really should have.

In 2007, the University at Albany, where the Giants held training camp for many years, named their practice field after Mara and Bob Tisch.

The Wilson football used in NFL games prior to the AFL merger (1941–1969) was nicknamed "THE DUKE" after Mara; the ball was named as such by George Halas, the owner and head coach of the Chicago Bears, to reward Tim Mara for arranging the contract that made Wilson the official supplier of footballs to the NFL.