In track & field, Dennard competed as a sprinter. He was the runner-up in the 100-meter dash at the 2010 GHSA 1A State Championships, where he took silver recording a personal-best time of 10.72 seconds.
Considered a two-star recruit by ESPN.com, Dennard was listed as the No. 166 wide receiver in the nation in 2010.
As a true freshman in 2010, Dennard played in six games with two starts, missing five games due to injury. As a sophomore in 2011, he played in 11 games, missing two due to injury, he finished the season with 42 tackles and three interceptions, two which came against Georgia in the Outback Bowl. As a junior in 2012, he started all 13 games, recording 52 tackles and three interceptions. He was a first team All-Big Ten selection. As a senior in 2013, he recorded 62 tackles and four interceptions, he won the Jim Thorpe Award.
Dennard was selected by the Cincinnati Bengals as the 24th pick of the first round. He signed a four-year, $8 million contract with $6.5 million guaranteed with the Bengals on June 12, 2014.
Dennard saw limited playing time in his rookie season, participating in just 41 snaps. His most notable achievement was forcing a fumble in a playoff game against the Indianapolis Colts that set up a Bengals field goal.
In week 6 of the 2015 season, Dennard recorded his first career interception in a win against the Buffalo Bills.
On November 27, 2015, he was placed on injured reserve.
Dennard's last name is pronounced as de-NARD. This pronunciation differs from that of his second cousin, Alfonzo Dennard due to a family dispute. Alfonzo, who is also a cornerback in the NFL, pronounces his last name DENN-erd.