Douglas debuted for Waikato in a match against Horowhenua-Kapiti in 2013 and to the end of the 2016 Mitre 10 Cup season had made 36 National Provincial Championship and Ranfurly Shield challenge appearances and scored 8 tries.
He was named co-captain of Canterbury for the 2018 Mitre 10 Cup season.
In 2019 Douglas made a return to the Crusaders for the 2019 Investec Super Rugby season after a stint at Italian club Benetton.