Thomas Kavanagh was born on 10 October 1898 at Gregg's Hill, Arklow, County Wicklow. He was a son of Denis Kavanagh and Julia Reilly. From an early age, Thomas lived at Rock Big, Arklow, in the household of his uncle and aunt, James and Elizabeth Dunne.
Thomas was born at Gregg's Hill, Arklow, on 10 October 1898. Registered on 19 October 1898 by Eliza Tyrrell, residing at Well Lane, Arklow. His father is recorded as Denis Kavanagh, a fisherman, and his mother as Julia Kavanagh, formerly Reilly.
Recorded as a 3-year-old nephew residing at House 8, Rock Big, Arklow Rural, in the household of his uncle James Dunne and aunt Eliza Dunne (nee Kavanagh).
Recorded as a 13-year-old single nephew living at House 10, Rock Big, Arklow Rural, with James and Elizabeth Dunne. He is noted as able to read and write.
Thomas's uncle, James Dunne, was working aboard a vessel as a fisherman under Thomas's command while residing at Abbey Terrace. Thomas was recorded as a fishing boat skipper operating out of Arklow, although he cannot be found in the 1926 census.