Pittsburgh Steelers

Reilly was eligible to be selected in the 2009 NFL Draft, but went undrafted. He signed a free agent contract with the Pittsburgh Steelers. Reilly completed 10-of-15 for 117 yards during the 2009 preseason, but was waived on September 5, 2009.^{[citation needed]}

Green Bay Packers

On November 19, 2009, Reilly was signed to the Green Bay Packers practice squad.^{[citation needed]}

St. Louis Rams

On December 9, 2009, he was signed off the Packers' practice squad by the St. Louis Rams. He was waived on May 4, 2010.^[4]

Seattle Seahawks

Reilly was claimed off waivers by the Seattle Seahawks on May 4, 2010. He was waived on May 18, 2010.^[5]

BC Lions

On July 26, 2010, it was announced that Reilly had signed a practice roster agreement with the BC Lions. On August 26, 2010, Reilly was activated by the Lions and spent the remainder of the year as the third-string quarterback.^[6] He dressed for all 18 games in 2011 as the third-string quarterback and shared in the Lions' 99th Grey Cup victory. He got his first pro start on October 19, 2012, against the Edmonton Eskimos due to an injury to Travis Lulay. Reilly completed 19 of 28 throwing attempts for 276 yards with two touchdowns and one interception, leading the Lions to a victory over the Edmonton Eskimos 39–19. The win clinched a first round bye for the BC Lions in the 100th Grey Cup Playoffs.^{[citation needed]}

Edmonton Eskimos

On January 31, 2013, Reilly was traded to the Edmonton Eskimos by the BC Lions; the trade included the exchange of the clubs' second round picks in the 2013 CFL Draft and the Lions receiving the Eskimos' second round pick in the 2014 CFL Draft.^[7] Entering the 2013 CFL season, Reilly was in open competition with Matt Nichols for the starting quarterback job.^[8] Nichols tore his ACL in preseason which made Reilly the starting QB for the season. On August 18, 2013, Reilly threw for over 500 yards in a losing cause, the fourth highest performance for yards passing in a single game in the history of the Eskimos football club. In his first season as a full-time starter in the CFL, Reilly threw for 4,207 yards, with 24 touchdowns and 18 interceptions. He also finished 5th in the league in rushing yards with 709. Despite his efforts, the Eskimos struggled all season finishing with a record of 4–14 and missing the playoffs.^{[citation needed]}

In the 2014 season, Reilly played in 15 regular season games, leading the Eskimos to the number two seed in the Western Division with a record of 12–6. After defeating the Saskatchewan Roughriders in the Western semi-finals, Reilly and the Eskimos were defeated by the Stampeders 43–18, ending their season. It was revealed after the game that Reilly had been playing with a broken bone in his foot and had been in great pain. The injury had been caused in a previous game during the regular season.^{[citation needed]}

Reilly's third season with Eskimos was once again hampered by injuries, missing 8 games. He played in the first game of the season, and the last 9; winning 8 in a row to finish the season as the first seed in the West Division. Reilly completed 214 of 329 pass attempts for 2,449 yards with 15 touchdowns and 10 interceptions (passer rating of 89.8).^{[citation needed]} On November 29, 2015, the Eskimos won the 103rd Grey Cup with a score of 26–20 over the Ottawa RedBlacks in Winnipeg, Manitoba. After the game, he received the Grey Cup Most Valuable Player award after completing 21-of-35 pass attempts for 269 yards, two touchdowns and no interceptions.^[9] On April 14, 2016, the Eskimos announced they had signed Reilly to a contract extension through the 2018 CFL season.^[10] The three-year deal is reportedly worth over $400,000 in 2016 and then bumps up to over $500,000 in following seasons.^[11] Reilly continued his stellar play in the following three seasons, throwing for over 5,500 yards each season while tossing 88 touchdowns and 43 interceptions.

Set to become a free agent in February 2019, Reilly had a workout with the Jacksonville Jaguars in mid-December 2018.^[12]

Return to BC Lions

On February 12, 2019, Reilly became a free agent and subsequently signed a four-year contract with the BC Lions later that day.^[13] Despite lofty expectations to start the season the Lions only won one of their first 11 games. Reilly was able to lead the Lions to four consecutive victories pulling the Lions into a playoff race with his former team. However, Reilly suffered a wrist injury early in Week 18 against the Eskimos who would win the match and eliminate the Lions from playoff contention.^[14] Reilly underwent surgery in the days following and was declared out for the remainder of the season.^[15]

In November 2020, Reilly filed a grievance against the BC Lions claiming a portion of his salary was guaranteed, even though the 2020 season was cancelled due to the COVID-19 pandemic.^[16] He reached a settlement with the team and subsequently re-signed to a new contract through the 2022 season on December 17, 2020.^[17] After beginning the 2021 season with lingering injury issues, Reilly finished the year with 12 starts in 13 games played and passed for a league-leading 3,283 yards. On January 24, 2022, the BC Lions announced that Reilly had retired.^[18]