Nicknamed "Bubbles", Obst was a back pocket specialist but occasionally ventured into the forward line and was used at times as a rover. In 1967 he was a surprise winner of the Magarey Medal, becoming the tenth Port Adelaide player to have won the award. He was a member of Port Adelaide premiership teams in 1959, 1962, 1963 and 1965. When he retired in 1972 he had played 205 games for the club as well as six interstate matches for South Australia.
Obst came from a famous Port Adelaide family; his father Ken, brother Peter and nephew Andrew all played with distinction for Port Adelaide.
Obst's grandson Brad Ebert is a current player with Port Adelaide in the AFL.