The son of former NHL defenseman Per Djoos was a regular for Brynas in the Swedish Hockey League at age 19. On May 16, 2014, he signed a three-year contract with the Washington Capitals, who had selected him in the seventh round (No. 195) of the 2012 NHL Draft.
Djoos played two full seasons with Hershey of the American Hockey League. He went from 22 points (eight goals, 14 assists) in 2015-16 to 58 points (13 goals, 45 assists) in 2016-17.