Following the 2015 season, in February 2016, Irwin was traded to Toronto FC in exchange for targeted allocation money, a third-round pick in the 2016 MLS SuperDraft and a conditional first-round pick in the 2017 MLS SuperDraft.[16] After featuring as the club's starting goalkeeper for the first part of the season, Irwin sustained in injury in July, and as a result, he was replaced by his deputy Alex Bono in the starting line-up by manager Greg Vanney;[17] Upon his return to action, Irwin later regained the starting spot for the remainder of the regular season and the Playoffs,[18] as Toronto went on to reach the 2016 MLS Cup Final. In the final, held at BMO Field on December 10, Toronto were defeated by Seattle Sounders FC 5–4 on penalties, following a 0–0 draw after extra time; Irwin was able to stop Álvaro Fernández's spot kick during the shootout, but misses from teammates Michael Bradley and Justin Morrow ultimately proved to be decisive.[19] On December 13, 2016, Irwin was selected by Atlanta United FC in the third round of the 2016 MLS Expansion Draft, but was immediately traded back to Toronto for Mark Bloom and allocation money.[20]
The following season, Irwin suffered a hamstring injury in Toronto FC's home opener, a 0–0 draw against Sporting Kansas City; as a result, Bono was once again promoted to the starting line-up in Irwin's absence,[21] and eventually established himself as the team's outright first-choice shot-stopper by September 2017, due to his performances, even after Irwin's return from injury.[22][23][24][25] In a rematch of the previous season's MLS Cup Final, on December 9, Toronto defeated Seattle 2–0 at home to capture the 2017 MLS Cup and complete an unprecedented treble of the MLS Cup, the Supporters' Shield, and the Canadian Championship.[26][27]
On December 6, 2022, Minnesota United FC announced it had signed Irwin to a two-year contract, beginning in 2023, in support of starting goalkeeper, Dayne St. Clair.[31]
^"Capital City wins out". Nepean Barrhaven EMC. October 6, 2011. p. 27.
^Desaulniers, Darren (October 17, 2011). "Surviving the Impact; Capital City FC advances into CSL semifinals". Ottawa Citizen. pp. B6.
^Desaulniers, Darren (October 24, 2011). "Headed for the final; Capital City FC advances to Canadian Soccer League title game". Ottawa Citizen. pp. C5.
^Barrs, Rory (October 30, 2011). "Just one goal short for Capital City FC; First-year team loses CSL final". Ottawa Citizen. pp. C1.
^"City FC Rookie Nets Award". Ottawa Citizen. November 16, 2011.
^"Eagles Get Past Battery". uslsoccer.com. United Soccer Leagues. July 6, 2012. Archived from the original on April 12, 2013. Retrieved February 22, 2013.