Unrein made his NFL debut in Week 1 of the 2011 season against the Raiders.[1] He made his first NFL start in Week 2 of the 2012 season against the Falcons. In a game against the Tampa Bay Buccaneers on December 2, 2012, Unrein lined up for the first time as at the fullback position.[2] He proceeded to catch his first career touchdown pass from quarterback Peyton Manning.[3][4]
On April 11, 2013, Unrein signed a one-year, $630,000 tender.[5]
The Broncos placed a one-year $1.431 million tender on Unrein on March 7, 2014.[6]
On September 24, 2015, the San Diego Chargers reinforced the tight end position, bringing back Kyle Miller nine days after he was waived on September 15. To make room, the team released Unrein.
Chicago Bears
Unrein was signed by the Chicago Bears on September 25, 2015. On November 9, 2015, he lined up at fullback against the San Diego Chargers. This was the first of many times he was used like this by the Bears. He ended the 2015 season with 32 tackles, two tackles-for-loss, and a sack.[8]
On March 12, 2016, Unrein was re-signed by the Bears to a two-year contract.[9] He appeared in 13 games and started nine in the 2016 season. He recorded one sack on the season, in Week 14.[10]
In 2017, Unrein started eight out of 12 games played, recording a career-high 32 tackles and 2.5 sacks.[11] He was placed on injured reserve on December 5, 2017.[12]
Tampa Bay Buccaneers
On March 16, 2018, Unrein signed a three-year, $10.5 million contract with the Tampa Bay Buccaneers.[13][14] He was placed on injured reserve on September 3, 2018, with a concussion.[15]
On March 13, 2019, Unrein was released by the Buccaneers.[16]