Harris initially went to the University of Wisconsin to play for the Badgers. After redshirting his freshman year, he transferred to Illinois State. In 2010, he was named to the Missouri Valley Football Conference all-newcomer team. In 2012, he started all thirteen games as the Redbirds reached the FCS national quarterfinals, and he was named to the all-MVFC first team. But before the 2013 season, he was dismissed from the Redbirds for conduct detrimental to the team.
Professional career
Oakland Raiders
Harris was selected by the Oakland Raiders in the seventh round of the 2014 NFL Draft with the 235th overall pick. On May 20, 2014, he signed his contract with the Raiders. On September 18, 2014, Harris was waived. On September 20, 2014, he was signed to the Raiders' practice squad. On December 24, 2014, he was elevated to the active roster. On September 5, 2015, he was waived. On September 9, 2015, Harris was re-signed to the practice squad. On October 24, 2015, he was elevated to the active roster. On October 31, 2015, he was waived again. On November 3, 2015, Harris was re-signed to the practice squad. On November 19, 2015, he was elevated to the active roster again. On May 16, 2016, Harris was released by the Raiders.
On June 1, 2016, Harris was signed by the Jets. On August 28, 2016, he was waived by the Jets.
Dallas Cowboys
On December 22, 2016, Harris was signed to the Cowboys' practice squad. He was released on January 10, 2017.
Denver Broncos
On January 25, 2017, Harris signed a reserve/future contract with the Broncos. On September 11, 2017 on Monday Night Football Harris saved the game for the Broncos with a late-game block of a field goal by Los Angeles Chargers rookie Younghoe Koo. Harris went on to have the most productive season of his career, recording 34 tackles, 3 passes defended, and 5.5 sacks, the last of which was good for second on the team behind teammate Von Miller. On November 25, 2018, Harris recorded his first career interception. Harris intercepted Ben Roethlisberger in the endzone to prevent a would-be game-winning touchdown. On March 7, 2019, the Broncos placed a second-round restricted free agent tender on Harris. In week 11 against the Minnesota Vikings, Harris sacked Kirk Cousins 3 times, one of which was a strip sack which was recovered by teammate A.J. Johnson in the 27–23 loss. In the final game of the season against the Oakland Raiders, he preserved the Broncos' 16-15 victory by knocking down Derek Carr's pass on what would have been the game-winning two-point conversion. On April 2, 2020, the Broncos re-signed Harris to a one-year, $3.25 million contract.
