Denver Broncos in 2018 Kelly was selected by the
Denver Broncos in the seventh round, 253rd overall, the last selection in the
2017 NFL draft (
Mr. Irrelevant). He was placed on the reserve/
non-football injury list after having offseason wrist surgery. Going into
mini-camps for the 2018 season, he would compete with 2016 first-round draft pick
Paxton Lynch for the backup quarterback role behind newly acquired
Case Keenum. On August 13, 2018, Kelly was promoted to second-team to act as Keenum's backup. In Week 6 of the 2018 season, Kelly appeared in his first NFL game, kneeling for a one-yard loss at the end of the first half. On October 24, 2018, the Broncos released Kelly following his arrest on suspicion of first-degree criminal trespassing. He allegedly entered a couple's place of residence after leaving teammate
Von Miller’s Halloween party. On March 20, 2019, Kelly pleaded guilty to misdemeanor second-degree criminal trespassing for the incident.
Indianapolis Colts On May 20, 2019, Kelly signed with the
Indianapolis Colts. He was suspended the first two games of the 2019 season for violating the NFL's personal conduct policy. After being reinstated from suspension, he was waived on September 18, 2019. He was re-signed to the team's
practice squad the next day. He was promoted to the active roster on November 9, 2019. On September 5, 2020, Kelly was waived by the Colts and signed to the practice squad the next day. He was released on September 30. After being released from the Colts, Kelly temporarily stepped away from his professional playing career and returned to East Mississippi where he briefly worked as an offensive coach.
Toronto Argonauts On February 11, 2022, Kelly signed with the
Toronto Argonauts of the
Canadian Football League (CFL). In the Argos first preseason game Kelly completed seven of 12 pass attempts for 78 yards. He completed eight of 15 pass attempts in his second preseason game, throwing for 85 yards with one touchdown and one interception. The Argos released
Antonio Pipkin as part of the team's final roster cuts, which promoted Kelly to the role of backup quarterback to veteran
McLeod Bethel-Thompson to begin the
2022 season. Kelly served as the backup quarterback for the entire season before being named the team's starting quarterback for the Argo's final match of the regular season. In the
109th Grey Cup, after Bethel-Thompson injured his throwing hand in the fourth quarter, Kelly came off the bench with the Argos trailing 23–17 and helped lead them to a 24–23 win against the
Winnipeg Blue Bombers. He completed four of six passes for 43 yards and rushed twice for 21 yards, including a 20-yard run to convert a second and 15 on the team's game-winning touchdown drive. Kelly started the
Argos 2023 campaign as the starting quarterback, with a 32–14 win over the
Hamilton Tiger-Cats. On August 31, 2023, Kelly and the Argos agreed to a three-year contract extension worth a total of $1.865 million, making him the highest paid player in the league. The team would go 16–2 though lost to the eventual champion Montreal in the East final. Following the season Kelly won the
CFL's Most Outstanding Player Award. On May 7, 2024, the CFL announced that Kelly was suspended for at least nine games after an investigation into allegations made against him and the Argonauts by a former strength and conditioning coach. On August 18, he was reinstated by the CFL on a "last-chance agreement" that requires him to follow a number of confidential conditions. Kelly played in nine games for the Argonauts, starting in eight, where he had 175 completions, 2,451 yards, 10 touchdowns, and eight interceptions. In his first playoff start since his disastrous playoff starting debut in 2023, Kelly completed 18 of 20 passes for 358 yards and four touchdowns, for an uncapped passer rating of 218.3, which was the second highest of any CFL game ever. In the East Final game against the
Montreal Alouettes on November 9, Kelly was involved in a play in which
Isaac Adeyemi-Berglund fell on his right leg, resulting in
tibia and
fibula fractures. He subsequently underwent surgery to repair the fractures and was given a recovery timetable of roughly six months. In his absence,
Nick Arbuckle started the
111th Grey Cup where the Argonauts defeated the Blue Bombers and Kelly won his second championship. Kelly began the
2025 season on the one-game injured list as the team had wanted him to practice with the team as he recovered. However, despite being listed as "week-to-week", he was later placed on the six-game injured list on July 27, 2025, with Arbuckle continuing as the starting quarterback. After Arbuckle was injured in September, Kelly remained off of the roster as the team's playoff hopes dwindled. He eventually sat out the entire season due to injury as the Argonauts missed the playoffs for the first time since 2019. == Professional statistics ==