On 7–12 June 1917 at St. Yves, Belgium, during the Battle of Messines, Private Carroll rushed the enemy's trench and bayoneted four of the occupants. He then noticed a comrade in difficulty and went to his assistance, killing another of the enemy. Next, he single-handedly attacked a machine-gun team, killing three of them and capturing the gun. Later, two of his comrades were buried by a shell; in spite of heavy shelling and machine-gun fire, he managed to rescue them.
Carroll was later severely wounded at Passchendaele in October 1917. His rehabilitation was successful but after briefly returning to his unit, the Australian Prime Minister Billy Hughes, then in England, arranged for furlough to Australia for Victoria Cross recipients to help recruiting in Australia.
It has been claimed that Carroll failed on three occasions to appear at Buckingham Palace for his Victoria Cross award ceremony and when he did turn up on the fourth occasion he took advantage of one of the entitlements of VC recipients to call out the Palace Guard. These stories first appeared in the Perth Daily News on 2 November 1927 and the source of the story would seem to be Carroll himself. He related the story while he was in hospital after an industrial accident in which one of his feet was amputated. Just out of surgery and still in pain he was interviewed by a reporter who does not seem to have checked the veracity of the stories.