Britt was pressed into the starting lineup as a true freshman in 2006. That season, he had a major role in one of the biggest wins in school history, which was the victory over Louisville.

Britt continued his stellar play in the 2007 season, making 62 receptions for 1232 yards and 8 touchdowns, averaging 19.9 yards per catch. Britt led all sophomores in Division I-A football in receiving yards and yards per reception, finishing 11th and 5th in those categories respectively for all of I-A. Britt also led the Big East conference in both categories in 2007, and was rewarded with a spot on the Big East’s All-Conference team, and was named by Rutgers as its 2007 offensive MVP.

Britt was named to the 2008 Associated Press Third Team All-America. Britt was also a selection for First Team All-Big East in 2008.

On January 3, 2009, Britt announced he would forgo his senior season at Rutgers University and declare himself eligible for the 2009 NFL Draft.

Britt was drafted in the 1st round (30th overall) of the 2009 NFL Draft. He was Rutgers’ first ever first-round pick. His first game against the Pittsburgh Steelers was solid as he caught four passes for 85 yards, including a 57-yard reception in a 13–10 loss. He scored his first touchdown on the receiving end of a Vince Young pass on November 23, 2009, against the Houston Texans.

On November 29, 2009, Britt caught a ten-yard game-winning touchdown pass in the back of the endzone from Young as time was expiring during a 20-17 victory over the Arizona Cardinals.

On April 12, 2011, Britt was arrested in New Jersey on three counts (including a felony) following an alleged car chase with police. The charges were later reduced. On June 7, Britt pleaded guilty to careless driving and was fined. On June 8, 2012, Britt was arrested in Hoboken, New Jersey, charged with resisting arrest.

Entering the 2012 season, Britt had 101 catches for 1,765 yards (17.48 YPC) and fifteen touchdowns. On October 24, 2010, Kenny caught 7 passes, three touchdowns and gained 225 yards in a 37–19 victory over the Philadelphia Eagles. These were the highest numbers put up by a Titans receiver since Drew Bennett caught 233 yards and three touchdowns against Kansas City on December 13, 2004, and the most yards ever against the Eagles.

On March 31, 2014, Britt signed a one-year deal with the St. Louis Rams. The contract was worth $1.4 million with $550,000 guaranteed on the condition that he made the Rams 53-man roster.

Britt re-signed with the Rams on a two-year, $9.125 million contract on March 13, 2015.

In the 2016 season, Britt became the first Rams wide receiver to reach 1,000 yards since Torry Holt in 2007.

On March 9, 2017, Britt signed a four-year, $32.5 million contract with the Cleveland Browns. Britt’s effort and commitment to play football came into question throughout the entire season. After recording just 18 catches in nine games, he was released by the Browns on December 8, 2017. It was also reported that Britt requested his release.

On December 13, 2017, Britt signed a two-year contract with the New England Patriots. The team then went on to Super Bowl LII where they would lose to the Philadelphia Eagles 41-33. Britt was inactive for the Super Bowl. On March 6, 2018, the Patriots decided to pick up Britt’s second-year option, retaining him for the 2018 season. Britt was released by the Patriots on August 22, 2018.