Justin Douglas was born and raised in Townsville, Queensland.[3]
At a junior level, Douglas represented his home state, Queensland, at all Australian Championships.[4]
In the Australian Hockey League, Douglas represented the Queensland Blades from 2013 to 2018, winning three titles.[5]
Following the disbandment of the AHL, Douglas was named in the Brisbane Blaze team for the inaugural tournament of the Sultana Bran Hockey One League, Australia's new premier domestic competition.[6]
Justin Douglas made his debut for the Australia U–21 side, the 'Burras', at the 2012 Sultan of Johor Cup, winning a bronze medal.[7]
In 2013, Douglas made a series of appearances for the Burras. His first tournament was the Junior Oceania Cup,[8] where Australia won a gold medal and automatic qualification to the Junior World Cup.[9] Following this, he appeared in a tour of Europe,[10] as well a test series against the Malaysia U–21 side.[11] His last appearance for the Australia U–21's came in December at the Junior World Cup, where the team finished fifth.[12]