Picked by the Adelaide Crows with pick 16 overall in the 2005 AFL Draft, he impressed playing for Glenelg in the SANFL in season 2006 before making his AFL debut in round 21 against cross-town rivals Port Adelaide in the local Showdown.
In June 2009, in the lead-up to Adelaide's clash with North Melbourne, Douglas had a scare when he began displaying symptoms consistent with the swine influenza pandemic, and was quarantined. On the night before the match, the test for Swine Flu came back negative; however, he did not play in the match, which Adelaide won comfortably. He returned to play the next match, although he was a shock omission a few weeks later against Fremantle, making way for returning captain Simon Goodwin.
In 2010, Douglas was given more responsibility in the midfield by head coach; Neil Craig. He relished the opportunity; winning the 2010 Malcolm Blight Medal (best and fairest award) and the Coaches Award in a standout year in which he averaged 21 disposals per game. He played all 22 matches in 2010 and also signed a new two-year contract with the club.