One of thirteen children of Hugh, a wheelwright and carpenter, and Mary (nee Willcox), Tom Coy was born at Galway, Ireland on 7 February 1893. The family later moved to Wexford.

After working for a cooper, he entered the service at HMS IMPREGNABLE on 26 April 1909 as a Boy Seaman 2nd Class, rising to 1st Class on 22 November 1909. His first ship was the battleship HMS QUEEN, followed by service in the armoured cruiser HMS ARGYLL, where he was rated Ordinary Seaman on his 18th birthday. He was rated Telegraphist in August 1911 while serving in the battleship HMS PRINCE GEORGE.

He was advanced to Leading Telegraphist in September 1914 and spent the early part of the war in the armed merchant cruisers OROPESA and PATIA. He started submarine training at HMS DOLPHIN in August 1916.

Tom Coy is remembered on the Plymouth Naval Memorial, the HMS E49 memorial at Baltasound, Unst, in the Shetland Islands and the Great War memorial at St Nicholas Collegiate Church, Galway.