Fagerson enrolled in the BT Sport Scottish Rugby Academy in 2015-16 as a Stage 2 player.[4] In 2016-17 he was promoted to Stage 3 earning a full time professional contract with the academy.[5] Stage 3 players are assigned to a professional club and Fagerson has been assigned to Glasgow Warriors for the 2016-17 season.
Fagerson made his debut for the Warriors in the pre-season match against Canada 'A' on 30 August 2016.[6] In a 63–0 win for the Warriors, Fagerson scored a try on his debut.[7]
Fagerson made his Pro12 debut for the Warriors against Ulster on 23 September 2016 when he replaced Ryan Wilson.[8]
Fagerson signed a professional contract with the Warriors on 28 September 2017, turning professional on 1 October 2017.[9] The contract runs for two and a half years meaning that Fagerson has committed to the club until at least 2020.[10]