Indianapolis Colts On May 3, 2017, Walker was signed by the
Indianapolis Colts as an undrafted free agent. He was waived on September 2, 2017, and was signed to the Colts'
practice squad the next day. He signed a reserve/future contract with the Colts on January 1, 2018. On September 1, 2018, Walker was waived by the Colts and was signed to the practice squad the next day. He spent time on and off the Colts practice squad before being released on December 26, 2018, but was re-signed three days later. He signed a reserve/future contract on January 13, 2019. On August 31, 2019, Walker was waived and signed to the practice squad the next day, only to be released two days later.
Houston Roughnecks In October 2019, Walker was drafted by the newly-formed
XFL for the 2020 season. The
Pittsburgh Steelers called the XFL office to ask if they could sign Walker in October 2019, but was blocked as he was already under contract with the league. He was then allocated to the
Houston Roughnecks prior to the
2020 XFL draft. In the Roughnecks' first game against the
Los Angeles Wildcats, Walker tossed four touchdowns, helping the team win a 37–17 victory. He was named the league's first ever Star of the Week for his performance. Walker's final game of the 2020 campaign was marked by some controversy after, while his team was leading the
Seattle Dragons 32–23, he mistakenly
kneeled on fourth down at his own 21-yard-line with three seconds remaining on the clock – officials either failed to notice or refused to deal with Walker's palpable timing error and declared the game over, thus depriving Seattle the opportunity to score a touchdown and potential three-point conversion to tie the game. The league later admitted it was a mistake, but declared that the result would stand. On March 20, 2020, the season was canceled due to the
COVID-19 pandemic. Walker finished the 2020 season with a 5–0 record, 1,338 passing yards and 15 touchdowns with four
interceptions. He led the league in both passing touchdowns and passing yards. He was placed on the reserve/other league list after signing with the
Carolina Panthers in March, which was later terminated after the league had fully suspended operations on April 10, 2020.
Carolina Panthers in 2021 On March 25, 2020, Walker signed a two-year contract with the Panthers worth up to $1.5 million, reuniting him with former
Temple head coach
Matt Rhule. On October 29, 2020, Walker came in for the Panthers during the third quarter against the
Atlanta Falcons after an injury to
Teddy Bridgewater. When playing, Walker only threw one pass completion for three yards to
Robby Anderson in his four pass attempts and was benched once Bridgewater was ready to play again. After Bridgewater injured his right knee in the fourth quarter of the Panthers' Week 10 game against the
Tampa Bay Buccaneers, Walker finished the game, throwing for two completions and 12 yards. With Bridgewater remaining injured, Walker made his first NFL start the following week against the Detroit Lions, throwing for 258 yards, one touchdown, and two interceptions in a 20–0 win. On January 10, 2022, Walker re-signed with the Panthers. Walker began to get playing time following
Baker Mayfield's injury in Week 5 against the
San Francisco 49ers. In Week 7, Walker threw for 177 yards and two touchdowns in a 21–3 win over the Buccaneers. In the Week 8 game against the
Atlanta Falcons, Walker completed a 64-yard touchdown pass to receiver
D. J. Moore that would have essentially sealed the game for Carolina. However, due to Moore taking his helmet off and drawing a flag, the game went into overtime after kicker
Eddy Piñeiro missed the extra point, although it was later determined that no flag should have been thrown because Moore was already off the field. The NFL's Senior Vice President of Officiating Administration,
Perry Fewell, defended the call in interviews, noting that at least two other Panther players removed their helmets while still on the field. Debate on the call only intensified, with public discussion shifting to whether or not "
in the field" includes the
end zone or not, furthermore pointing out that Moore's number was the only one attributed with the penalty. The NFL Rulebook has since been updated: "...
by a player in the field of play or the end zone." The Panthers would go on to lose the game 37–34 in overtime.
Chicago Bears On March 16, 2023, Walker signed a two-year contract with the
Chicago Bears. On August 27, 2023, he was released by the team.
Cleveland Browns On August 30, 2023, Walker was signed to the
Cleveland Browns' practice squad. He was elevated to the active roster on September 30 ahead of the Browns Week 4 game against the
Baltimore Ravens. Walker was again elevated to the active roster and named the starter for the Browns' Week 6 game against the
San Francisco 49ers following an injury to
Deshaun Watson and a poor game by
Dorian Thompson-Robinson. In his first start, Walker led the Browns to victory over San Francisco with a final score of 19–17. In Week 7, Walker entered the game again due to an injury to Watson, throwing for 178 yards and leading the Browns to a 39–38 last-minute win over the Colts. On October 25, the Browns signed him to their active roster. Walker started the Week 8 game against the
Seattle Seahawks, completing 15 of 31 passes (48.4%) for 248 yards, one touchdown, and two interceptions in a 24–20 loss. He was waived by the Browns on December 9, and re-signed to the practice squad four days later. On December 26, Walker was signed to the active roster again.
Seattle Seahawks On June 10, 2024, Walker signed with the
Seattle Seahawks. He was released on August 27.
Calgary Stampeders On October 8, 2024, Walker was signed to the practice roster of the
Calgary Stampeders of the
Canadian Football League. He was released on October 27, one day after the end of the regular season. He was later re-signed on November 11. Walker dressed in 13 games, starting one, in 2025 as the backup to
Vernon Adams. He changed his jersey number from 2 to 11 in the following offseason. On April 30, 2026, Walker announced his retirement. ==Career statistics==