[3] Dempsey played domestically in Australia for the North Harbour Rays who compete in the National Rugby Championship.

Of the move to the Warriors, Dempsey stated:[5] The history that Glasgow has with fast-paced footie – with quick ruck speed – is something which very much suits my game.

[4] He was capped for Australia against Italy, coming off the bench at Lang Park in Brisbane on 24 June 2017.

[8][9] Dempsey was a member of the Wallabies 2019 Rugby World Cup squad[10] which were knocked out in the quarter-finals in Japan,[11] but did not play for Australia after that.

[12] After a three-year stand-down period from international rugby, Dempsey made his debut for Scotland on 29 October 2022 against Australia, the country he previously played for.