Jenkins attended Terry Parker High School in Jacksonville, Florida. He finished his junior year with 32 catches for 500 yards, and also rushed for another 251 yards on 40 carries in 2007. As a senior, he hauled in 41 passes for 515 yards, scoring four touchdowns. He was named to Scout.com's Florida Top-50 team. He was ranked the 59th-best recruit in the state of Florida and the No. 53 wide receiver nationally by Rivals.com. He was also named to the Atlanta Journal Constitution's Super Southern 100 as the 10th-best wide receiver.
He was also a standout sprinter on the track team. In 2006, he posted a personal-best time of 10.75 seconds in the 100-meter dash at the District Meet.
In his first three seasons (2008–2010), he totaled 1,849 all-purpose yards, including 1,156 receiving yards and 694 return yards. On October 1, 2011, he had a career-best performance against Northwestern, with 12 catches for 268 yards and three touchdowns. His performance against Northwestern broke the Illinois single-game receiving record, ranks fourth in Big Ten Conference history, and earned him Big Ten Offensive Player of the Week after the Northwestern game. Through the first 11 games of his senior season, Jenkins had 1,166 receiving yards and seven touchdown receptions.
As of November 20, 2011, Jenkins's 1,166 receiving yards during the 2011 season ranked second in the Big Ten Conference and 11th among NCAA Division I FBS players. At the conclusion of the 2011 season, Jenkins was named First Team All-Big Ten by both the coaches and media.
Jenkins was drafted 30th overall in the 2012 NFL Draft by the San Francisco 49ers.
Although healthy all season, Jenkins was active for only three of the 49ers 16 regular season games. In his rookie regular season he played in only 37 offensive snaps and was targeted with a pass just once, which he dropped.
On August 19, 2013, Jenkins was traded to the Kansas City Chiefs for wide receiver Jon Baldwin.
During a Thursday night game on September 19, 2013 against the Philadelphia Eagles, Jenkins recorded his first career reception, thrown by former 49ers teammate Alex Smith. The reception was good for 6 yards. His first reception came 511 days after he was drafted.
On February 17, 2015, Jenkins was released by the Chiefs.
On May 26, 2015, Jenkins was signed by the Dallas Cowboys, but was released prior to the start of the regular season on September 5, 2015.