In 1972 Harris was named the league's Rookie of the Year by both The Sporting News and United Press International. In that season he gained 1,055 yards on 188 carries, with a 5.6 yards per carry average. He also rushed for 10 touchdowns and caught 3 touchdown passes. He was popular with Pittsburgh's large Italian-American population: his fans dubbing themselves "Franco's Italian Army" and wore army helmets with his number on them. In his 13 professional seasons, Harris gained 12,120 yards on 2,949 carries, a 4.1 yards per carry average, and scored 91 rushing touchdowns. He caught 307 passes for 2,287 yards, a 7.4 yards per reception average, and 9 receiving touchdowns. Harris's 12,120 career rushing yards rank him 12th all time in the NFL, while his 91 career rushing touchdowns rank him 10th all time tied with Jerome Bettis.

This Riddell Pittsburgh Steelers mini helmet was signed in gold by Harris and includes a Great Moments COA.