He was also on the school's track & field team, where he was a standout sprinter and long jumper. He placed 5th in the long jump event at the 2010 GMAC Qualifiers, with a jump of 6.60 meters. In 2011, he placed 4th in the 100 meters at the 3rd Annual Miramar Invitational, recording a career-best time of 10.62 seconds. He finished 3rd in the 200 meters at the FHSAA 3A District 16, with a time of 22.31 seconds.

Johnson attended and played college football at the University of Miami from 2012 to 2014. In his freshman season, he rushed for 947 yards on 139 carries with ten touchdowns and caught 27 passes for 221 yards and one touchdown. He also threw an additional touchdown in a 41–40 loss to Virginia. He also played a major role on special teams, where he returned 28 kicks for two touchdowns. In 2012, Johnson won both the ACC Rookie of the Year and Offensive Rookie of the Year awards. He became the first Miami Hurricane to win both awards. In 2013, Johnson joined the Miami indoor track team, posting a personal-best time of 6.92 seconds in the 60 meters at New Mexico Classic. Johnson's sophomore campaign with the Hurricane's football team came to an abrupt end on November 2, 2013, when he broke his ankle against arch-rival Florida State. Miami lost that game 41–14. Through eight games, Johnson rushed for 920 yards on 145 carries, with six touchdowns. He also had four catches for 77 yards. Johnson returned from the injury his junior season in 2014 to play in all 13 games. During the season, he passed Ottis Anderson to become the Hurricanes' all-time rushing yards leader. He ended the 2014 season with 1,652 yards and 10 touchdowns.

Johnson suffered a hamstring injury on August 1, the first day of the Browns' training camp. He sat out the next 10 days, and the team said he would not play in the first preseason game against the Washington Redskins at FirstEnergy Stadium on August 13. During Johnson's first pre-season appearance, he was diagnosed with a concussion and was removed from the game. On September 13, Johnson made his NFL debut, running for 22 yards on 7 carries against the New York Jets. On October 4, Johnson caught 9 passes for a career-high 85 yards and his first touchdown of his career. Johnson caught a 34-yard touchdown. On October 25, Johnson caught 7 passes for 73 yards against the St. Louis Rams. On November 1, Johnson recorded a 52-yards reception against the Arizona Cardinals. On November 5, Johnson scored his second touchdown of his career against the Cincinnati Bengals, a 12-yard reception. On December 13, Johnson ran for 78 yards on 13 carries against the San Francisco 49ers. On December 20, Johnson ran for a 39-yard gain against the Seattle Seahawks. Johnson caught a pass for 22 yards. Johnson finished the 2015 season with 379 rushing yards on 104 carries and 534 receiving yards on 61 receptions and two touchdowns. Johnson's 61 receptions are the 2nd-most by a Browns rookie, tied with wide receiver Greg Little. Among rookies, Johnson was ranked 12th in rushing yards and was one of twelve running backs to break 300 receiving yards. Among rookies, Johnson ranked 1st in receptions and receiving yards among rookie running backs and 2nd in receptions overall, just under Oakland Raiders' Amari Cooper. Johnson was ranked 6th overall among rookies in receiving yards and was 1 of 6 rookies to break 500 yards receiving.

On September 18, 2016, Johnson recorded a 28-yard reception against the Baltimore Ravens. On September 25, Johnson ran for 69 yards on 10 carries against the Miami Dolphins. On October 16, Johnson scored his first rushing touchdown against the Tennessee Titans. On October 30, Johnson caught 6 passes for a season-high 87 yards against the New York Jets. In addition, he recorded a 32-yard reception.

Johnson remained in the Browns' backfield in the 2017 season. In Week 15, against the Baltimore Ravens, he became the first NFL running back since Herschel Walker in 1986–1988 to record at least 500 receiving yards in each of his first three seasons. Overall, he finished the 2017 season with 348 rushing yards, four rushing touchdowns, 74 receptions, 693 receiving yards, and three receiving touchdowns.