An American football running back for the Tennessee Titans of the National Football League. Johnson is widely regarded as one of the fastest players in the NFL and as a Pro Bowl starter in his first three seasons, he has established himself as one of the elite running backs in the league.

Unheralded out of Orlando, Florida, Johnson emerged as a senior at East Carolina where he broke out for 2,960 all-purpose yards and 24 touchdowns. He was drafted by the Titans 24th overall in 2008, after running a record-tying 4.24 sec in the 40-yard dash at the NFL Combine. In his second year of professional football, he won the NFL rushing title with 2,006 yards (only the sixth player ever to break 2,000), and broke Marshall Faulk's record of total yards from scrimmage with 2,509. He was named the NFL's Offensive Player of the Year in 2009 and earned the nickname CJ2K.

Johnson played football at Olympia High School in Orlando. Johnson was also a track star at Olympia High. In his senior year, he finished second in the 100 metres at the 2004 Florida 4A state championships behind 2008 Olympic bronze medalist Walter Dix. In addition, Johnson also finished his senior season posting personal bests of 10.50 (the nation's 10th fastest in 2004) and 21.30 (the nation's 24th fastest in 2004) in the 100 metres and 200 metres respectively. His junior year he qualified for the finals of the Florida State meet with a preliminary time of 10.83. Walter Dix won the event with a 10.46 in the finals, Johnson placed 4th with a time of 10.66.

Considered only a two-star recruit by Rivals.com, Johnson was not ranked among the nation's top running back prospects in 2004. He selected East Carolina over Eastern Kentucky and UConn.

Prior to the NFL Scouting Combine, Johnson was projected a second to third round draught pick in the 2008 NFL Draft. However, at the combine he registered a 4.24-second time and tied the all-time mark set by Rondel Melendez, a wide receiver from Eastern Kentucky, in 1999—the first year the combine used electronic timers. Johnson was also fifth highest among running backs in the vertical jump with a 35-inch jump. His 10-foot, 10-inch broad jump was third best among the running backs.

After participating in the Titan summer training camp prior to the 2012 season, Johnson has initially struggled during his first two games of the 2012 season gaining just 21 yards on a total of 19 rushing attempts. Johnson during recent interviews appears to be frustrated with the new direction Titan's offensive coordinator Chris Palmer is running, electing to bring a more run-and-shoot offensive scheme to the Titans and not focusing on establishing the rushing attack. However, he seems to be having a career revival, with 862 yards and 4 TDs through Week 10.