Born in Minneapolis, Minnesota, Gillman played college football at Ohio State University under legendary coach Francis "Shut the Gates of Mercy" Schmidt. He was an All-Big Ten end in the early 1930s. Always deeply interested in the game, while working as a movie theater usher, he would remove the football segments from newsreels that the theater would show, so that he could take them home and study them on a projector he had bought for his own use. It was this dedication to filmed football plays that made Gillman the first coach to study game footage, something that all coaches do today.
Gillman played one year in the National Football League for the Cleveland Rams, then became an assistant coach at Denton University and Ohio State, then head coach at Miami University of Ohio and at the University of Cincinnati. He returned to the NFL as a head coach, with the Los Angeles Rams, where he led the team to the NFL's championship game, then he moved to the American Football League, where he coached the Los Angeles and San Diego Chargers to five Western Division titles and one league championship in the first six years of the league's existence. His greatest coaching success came after he was persuaded by Barron Hilton, then the Chargers' majority owner, to become the head coach of the American Football League franchise he planned to operate in Los Angeles. When the team's general manager, the late Frank Leahy, became ill during the Chargers' founding season, Gillman took on additional responsibilities as general manager. As the first coach of the Chargers, Gillman gave the team a personality that matched his own. He was mercurial. Gillman's concepts formed the foundation of the so-called "West Coast offense" that pro football teams are still using.
He had much to do with the American Football League being able to establish itself. Gillman was a thorough professional. In order to compete with him, his peers had to learn pro ways. They learned, and the American Football League became the genesis of modern professional football.
"Sid Gillman brought class to the AFL," Oakland Raiders managing general partner Al Davis once said of the man he served under on that first Chargers team. "Being part of Sid's organization was like going to a laboratory for the highly developed science of professional football." Through Gillman's tenure as head coach, the Chargers went 87-57-6 and won five AFL Western Division titles. In 1963 they captured the only league championship the club ever won by outscoring the Boston Patriots, 51-10, in the American Football League championship game in Balboa Stadium. That game was a measure of Gillman's genius. He crafted a game plan he entitled "Feast or Famine" that used motion, then seldom seen, to negate the Patriots' blitzes. His plan freed running back Keith Lincoln to rush for 206 yards. In addition to Lincoln, on Gillman's teams through the '60s were these Hall of Famerss: wide receiver Lance Alworth; offensive tackle Ron Mix; running back Paul Lowe; quarterback John Hadl; and defensive linemen Ernie Ladd and Earl Faison. Gillman was one of only two head coaches to hold that position for the entire 10-year existence of the American Football League.
Gillman approached then-NFL Commissioner Pete Rozelle in 1963 with the idea of having the champions of the AFL and the NFL play a single final game, but his idea was not implemented until the Super Bowl game was played in 1967. His final coaching job was in the 1980s, when he coached the Los Angeles Express of the now-defunct United States Football League.
Gillman's influence on the modern game can be seen by listing the current and former coaches and executives who either played with him or for him:
Besides the downfield pass, watching filmed footage, and the idea of the Super Bowl, Gillman also came up with the idea of putting players' names on the backs of their uniforms. Gillman is a member of the American Football League Hall of Fame.