He made the Chiefs' roster in 1964 as a rookie free agent out of Southern and wound up as the team's second-leading rusher that season with 567 yards and four touchdowns on 105 carries. He played in the AFL All-Star Game after his rookie campaign. He gained 627 yards, second-most on the team, in 1965, even though he did not complete the season, dying after the 12th game. He was nicknamed "The Truck." His number 36 is retired.
Through Hill's inspiration, the Chiefs created the Mack Lee Hill Award, which is given each season to the team's most outstanding rookie.