Denis was a son of David and Emily Callinan. When he enlisted in Sydney in September 1916 he stated he was born at Inverell. He was a Jockey living at Redfern in 1915.
Denis joined the 55th Battalion, 7th Reinforcement and left Australia on HMAT A11 Ascanius in October 1916, arriving in England just before Christmas. Two months later he was sent to France and then transferred to the 18th Battalion. Whilst helping dig trenches in April 1918 he was hit by a shell and taken to a Casualty clearing station where the following day he died of his wounds. He was twenty nine years old.
Denis was buried at Vignacourt British Cemetery in France. His personal effects were returned to his father and included photos, letters, pipe and scissors.