Frank Leahy was born on August 27, 1908 in O’Neill, Nebraska. Leahy was born in O'Neill, Nebraska and graduated from Winner High School in Winner, South Dakota where he was a football standout. 

Leahy played at Notre Dame under Rockne in 1929, but a knee injury in 1930 ended his playing career. While he was recuperating from a knee operation, he shared a hospital room with Rockne, who was struck with Leahy’s football acumen and made him informally a coach of the tackles until his graduation in 1931. Leahy graduated from Notre Dame in 1931 and went to Georgetown as line coach in 1931, then to Michigan State the following year to take a similar position.  He took over as line coach at Fordham in 1933 and stayed until 1938 under Jim Crowley, coaching the famed "Seven Blocks of Granite" from 1935-37, when the Rams lost only two combined games.

In 1939, Leahy went to Boston College as head coach, guiding the Eagles to a 20–2 record including an undefeated 1940 season capped off with a win in the 1941 Sugar Bowl. Although he had recently signed a contract renewal at Boston College, Leahy accepted the head coaching position at his alma mater, Notre Dame. He tried without success to get out of his BC contract. He pleaded to the school's vice president. When that didn't work, he went to the mayor of Boston. Then the governor of Massachusetts. Then, at a press conference, he told 50 reporters what the South Bend Tribune called "the biggest lie of his life". Leahy stated: "Gentlemen I've called you all here today to inform you that I recently received my release from my coaching contract. With the release went the good wishes and benediction of Boston College." Leahy stepped away, and the buzzing group of reporters battled for phone lines. A phone call came in for Leahy, and he took it. The vice president of Boston College was on the line. "Coach Leahy," he barked. "You may go wherever you want, and whenever you want. Good-bye."

He entered the Navy in 1944 and was discharged as a lieutenant. He returned to Notre Dame for the 1946 season and stayed until resigning for health reasons in 1954. While at Notre Dame, Leahy had six undefeated seasons, five national championship teams and an unbeaten string of 39 games in the late 1940s. 

His teams at the University of Notre Dame won 87 games, lost 11, and tied 9. His career winning percentage of .864 (107–13–9) ranks second in the history of first-division college football to that of Knute Rockne, a predecessor at Notre Dame.

He served as the general manager of the AFL's Los Angeles Chargers during their inaugural season in 1960 and was inducted into the College Football Hall of Fame as a coach in 1970.  Though nearly as successful as Rockne, his teams in the late 1940s were more dominant than Rockne’s best. Leahy lacked Rockne’s personal charm and skill in cultivating sportswriters; thus, he never enjoyed his predecessor’s popular affection. After his retirement from football, he was a business executive, a sports columnist, and a television commentator.