As a collegiate football player at the University of Texas at Austin, he won the Heisman Trophy in 1977 and led the nation in rushing with 1,744 yards. In 1977, he became the first recipient of the Davey O'Brien Memorial Trophy which was awarded to the most outstanding player in the now-defunct Southwest Conference. He was also a consensus All-America choice in 1977. Additionally, he was a First-team All-America selection by the AFCA in 1975. He was selected as the Southwest Conference running back of the year in each of his college seasons and finished with 4,444 career rushing yards.
Campbell was the first draft pick overall in the 1978 NFL Draft by the Houston Oilers, who signed him to a six-year, $1.4 million contract. Campbell's agent was Michael Trope. That year Campbell was named the Offensive Rookie of the Year by the Associated Press as well as the NFL Offensive Player of the Year. The Luv Ya Blue era in Houston was due mostly to Campbell's running ability and Coach Bum Phillips' "good ole boy" personality.
Campbell possessed a rare combination of speed and power, and was a prolific running back from 1978 through 1985. His outstanding single-season performance in 1979 earned him All-Pro, Pro Bowl, and NFL Offensive Player of the Year honors. It was also the second of three consecutive seasons in which he led the league in rushing. Only Jim Brown had previously accomplished that feat. Campbell led the NFL in rushing in 1978, 1979, and 1980. He played in five Pro Bowls and finished his career with 9,407 yards and 74 touchdowns rushing along with 806 yards on 121 receptions. In 1980, Campbell's best year in the NFL, he ran for 1,934 yards including four 200-yard rushing games, including a personal best 206 yards against the Chicago Bears. Despite playing against stacked defenses Campbell managed to average 5.2 yards per carry and score 13 rushing touchdowns in 1980 alone.