After his college career at the University of Louisville, Unitas was drafted by the Pittsburgh Steelers of the NFL, but was released before the season began. In 1956 Unitas joined the Baltimore Colts NFL team. The Colts won the NFL championship under his leadership in 1958, by defeating the New York Giants in sudden death overtime. It was the first overtime game in NFL history, and is often referred to as the "greatest game ever played". The game has been credited for sparking the rise in popularity of football during the 1960s. Unitas then led the Colts to a repeat championship in 1959. Later in his career, although he was injured through most of the 1968 season, he came off the bench to play in the Super Bowl III, which the Colts lost. Unitas was also injured during the Super Bowl V, but he did throw a key touchdown pass in the game that helped lift the team to victory.
Unitas set many passing records during his career. He was the first quarterback to throw for more than 40,000 yards, despite playing during an era when NFL teams played shorter seasons of 12 or 14 games (as opposed to the 16 game seasons that are played today). He also threw a touchdown pass in 47 consecutive games between 1956 and 1960, a record that still stands today.