He was a member of the St. Louis Rams, Miami Dolphins, Cleveland Browns, Denver Broncos, Seattle Seahawks and Tennessee Titans.

He played college football for the Southern Miss Golden Eagles, where he began his career as a walk-on, he redshirted the 2007 season and became the starter a year later.

Davis later served as the offensive coordinator for the Auburn Tigers but left the program within two months and coaching no games.

Davis attended West Lauderdale High School in Collinsville, Mississippi, where he was coached by Stan McCain.

During his career, Davis received all-area honors, was named best offensive back in the district and played in the Mississippi/Alabama All-Star game.

His total offense average was the highest among freshmen quarterbacks in the country, ahead of the likes of Kellen Moore of Boise State (265.9) and Robert Griffin of Baylor (244.5).

[12] On November 30, Southern Miss went on the road to face the eventual C-USA and Liberty Bowl champion Central Florida and their highly rated defense.

Davis responded by completing 21–34 passes for 264 yard and 4 scores, leading the Golden Eagles to a 31–21 road upset over the ranked Knights.

[17] Heading into his senior season, Davis had either broken or was on the verge of breaking nearly every passing record in Southern Miss history.

[25] Prior to the Draft, Bleacher Report's Tyler Ward named Davis as one of his eleven potential late-round sleepers.

[31] In the first week of the 2014 NFL season against the Minnesota Vikings, Davis entered the game at the start of the second half in relief of starter Shaun Hill.

A week later, due to Hill's injury, Davis made his NFL starting debut on September 14, in a winning effort against the Tampa Bay Buccaneers.

Following the Rams' 28–26 upset win over the defending Super Bowl champion Seattle Seahawks in Week 7, former All-Pro quarterback and legend Brett Favre tabbed Davis as a potential Tom Brady or Kurt Warner of the future, both of whom won Super Bowls despite a bleak start to their NFL careers.

During the victory, Davis completed 17-of-20 passes,[32] the best completion percentage in NFL history against a defending Super Bowl champion; the former Southern Miss QB also added 152 passing yards and two touchdowns, one of which ultimately sealed their victory after Davis successfully led an 80-yard drive.

After two interceptions and a lost fumble in the 4th quarter against the Arizona Cardinals in early November, Davis was benched in favor of Hill.

[39] He played again in the season finale against the Pittsburgh Steelers after Manziel was ruled out with a concussion, going 24 for 46 with no touchdowns and a pair of interceptions in a 28–12 loss.

On September 25, 2018, Davis was signed by the Tennessee Titans after backup Blaine Gabbert suffered a concussion against the Jacksonville Jaguars in Week 3.