Green Bay Packers (first stint) Not selected in the
2016 NFL draft, Callahan signed as a free agent with the
Green Bay Packers on May 6. He threw for 499 yards, three touchdowns, and zero interceptions in the
preseason, earning him a spot on the Packers'
53-man roster. He was released by the Packers on October 13.
New Orleans Saints On October 14, Callahan was claimed off waivers by the
New Orleans Saints, and waived by the team on October 22.
Cleveland Browns Callahan was claimed off waivers by the
Cleveland Browns on October 24, and released by the team on November 28.
Green Bay Packers (second stint) On December 2, Callahan was signed to the Packers' practice squad, and was promoted to the active roster on December 17, 2016. On September 2, 2017, Callahan was waived by the Packers and was signed to the practice squad the next day. After starter
Aaron Rodgers suffered a broken collarbone in Week 6 against the
Minnesota Vikings, head coach
Mike McCarthy stated that
Brett Hundley would take over as starter and Callahan would be Hundley's backup. Callahan was promoted to the active roster the following day. On December 16, 2017, with Hundley still maintaining his position as the Packers' second-string quarterback and the return of
Aaron Rodgers from
injured reserve, Callahan was cut to make room for Rodgers. However, three days later on December 19, the Packers re-signed Callahan after Rodgers was placed back on injured reserve. Callahan made his NFL debut on December 31, completing 5 of 7 passes for 11 yards. On April 30, 2018, Callahan was waived by the Packers.
Philadelphia Eagles On May 7, 2018, Callahan signed a two-year contract with the
Philadelphia Eagles. He was waived on September 1, 2018.
Tampa Bay Buccaneers On January 3, 2019, Callahan signed a reserve/future contract with the
Tampa Bay Buccaneers. On April 26, 2019, the Buccaneers waived Callahan.
Baltimore Ravens On July 29, 2019, Callahan was signed by the
Baltimore Ravens. He was waived during final roster cuts on August 30, 2019.
Detroit Lions On November 30, 2019, Callahan was signed to the
Detroit Lions. His practice squad contract with the team expired on January 6, 2020.
Seattle Dragons Callahan was selected by the
Seattle Dragons of the
XFL during the
2020 XFL draft's open phase. He signed a contract with the team on January 13, 2020. He was waived during final roster cuts on January 22, 2020.
Team 9 Callahan was signed to the XFL's
practice squad team, referred to as
Team 9, on January 30, 2020. He had his contract terminated when the league suspended operations on April 10, 2020. ==Career statistics==