Mayza pitched the entire 2015 season with the Single–ALansing Lugnuts. He made 26 appearances for the Lugnuts, and posted a 3–2 record, 3.07 ERA, and 62 strikeouts in 552⁄3 innings pitched.[7] Mayza continued to progress through the Blue Jays organization, beginning the 2016 season with the High–ADunedin Blue Jays. In June, he earned a promotion to the Double–ANew Hampshire Fisher Cats, where he finished the year. Mayza made a career-high 42 pitching appearances in 2016 and went 3–3 with a 2.25 ERA and 65 strikeouts in 64 total innings.[7] On January 19, 2017, Mayza was invited to Major League spring training.[8] He was assigned to Double-A New Hampshire to begin the 2017 season. After 29 appearances, Mayza was promoted to the Triple–ABuffalo Bisons. He made 11 relief appearances, posting a 0.93 ERA, before his first promotion to the Majors.[9]
On August 14, 2017, Mayza was promoted to the major leagues for the first time.[9] He made his major league debut on August 15, pitching a scoreless 9th inning in a 6–4 loss to the Tampa Bay Rays and recording his first major league strikeout against Peter Bourjos.[10] Mayza was credited with his first major league win on September 12, when he pitched the bottom half of the 9th inning before the Blue Jays walked off the Baltimore Orioles 3–2.[11]
Mayza split the 2018 season between the major leagues and the Buffalo Bisons. In 37 games for the Blue Jays, he posted a 2–0 record with a 3.28 ERA and 40 strikeouts over 352⁄3 innings.[12]
On September 13, 2019, in the 10th inning in a game against the New York Yankees, Mayza threw a pitch behind Didi Gregorius and immediately crumpled to the ground in pain. The next day, it was revealed he had torn his UCL and would undergo Tommy John surgery.[13] In 68 relief outings for Toronto in 2019, he compiled a 4.91 ERA with 55 strikeouts across 51+1⁄3 innings of work. Mayza was outrighted off the Blue Jays roster on November 20, 2019.[14] He spent all of 2020 recovering from the surgery.
On April 1, 2021, Mayza was selected to the 40-man roster.[15] That year, he recorded a 3.40 ERA and 57 strikeouts across 61 appearances for Toronto. On September 28, 2022, Mayza gave up Aaron Judge’s 61st home run, tying an American League record. He made 63 total appearances for the Blue Jays in 2022, compiling an 8–1 record and 3.14 ERA with 44 strikeouts across 48+2⁄3 innings pitched.[16]
On January 13, 2023, Mayza signed a one-year, $2.1 million contract with the Blue Jays, avoiding salary arbitration.[17] He made 69 appearances for Toronto in 2023, compiling a 1.52 ERA with 53 strikeouts across 53+1⁄3 innings of work.
Mayza began the 2024 campaign out of Toronto's bullpen, and struggled to an 8.03 ERA with 16 strikeouts across 24+2⁄3 innings pitched.[18] On June 29, 2024, Mayza was designated for assignment by the Blue Jays.[19] He was released by the organization on July 5.[20]
New York Yankees
On July 10, 2024, Mayza signed a minor league contract with the New York Yankees.[21] In 9 games for the Triple–A Scranton/Wilkes-Barre RailRiders, he posted a 2.16 ERA with 8 strikeouts. On August 16, the Yankees selected Mayza's contract, adding him to their active roster.[22]