Mr Thomas David O’Connor was born at 5 Mount Pleasant Avenue in Limerick, Co Limerick, Ireland on 31 January 1895. He was the son of Thomas Joseph O’Connor, an upholsterer, and Helena “Nellie” Maher; his father also hailed from Limerick whilst his mother had been born in London to Irish parents. He had at least six siblings.

Thomas came from a long-line of staunch Irish nationalists and several in his family were involved in Republican-leaning Irish political groups as well as the Gaelic revival; as a youth Thomas was a member of Na Fianna Éireann, an Irish nationalist youth organisation founded by Belfast-born Quaker and Irish Republican Bulmer Hobson. 

Sometime after 1898 Thomas and his family left Limerick and settled in Dublin where in 1901 they lived at Sherrard Street in Rotunda. At some point Thomas resettled in or nearby Liverpool where he began working at sea and in April 1912 he was a scullion aboard the Carpathia when that ship rescued the survivors of the Titanic disaster. 

After the Titanic disaster, O’Connor became more heavily involved in Irish Republican activities; as a member of the I.R.B. (Irish Republican Brotherhood) he acted as an important courier between 1912 and the Easter Rising in 1916, taking dispatches from Dublin to the New York Clan na Gael, an Irish Republican organisation in the USA. He was reportedly close to several prominent participants and leaders of the 1916 insurrection, including Tom Clark, Michael Collins and Seán Mac Diarmada. 

O’Connor took part in the Easter Rising in Dublin over the Easter week in 1916 and, like many of his fellow revolutionaries, was imprisoned in Frognoch Internment Camp in Merionethshire, Wales. After his internment he became a captain in the Irish Republican Army during Ireland’s War of Independence. Following that conflict, O’Connor sided with the anti-treaty faction of Sinn Féin, which was determined to deliver a singular whole-Ireland republic. The Anglo-Irish Treaty had culminated in the partition of Ireland, resulting in two states, Northern Ireland and the Irish Free State (modern-day Republic of Ireland), a settlement that the anti-treaty alliance vigorously opposed.

In April 1922 O’Connor travelled to the USA aboard the Aquitania as part of a delegation of anti-Treaty Irish Republicans; accompanying him was Irish Republican and Easter Rising veteran Countess Constance Markievicz, as well as Kathleen Barry, the sister of IRA man Kevin Barry (d. 1920 aged 18), the last man hanged in Ireland under UK sovereignty. Markievicz, like O’Connor, was vehemently anti-treaty and O’Connor took to the US press to correct what he saw as misrepresentations of her positions in the numerous lectures she gave throughout the US:

Sir—On the front page of your issue of Tuesday April 11 you have a photograph of Countess Markievicz and Miss Kathleen Barry. In the caption you state these ladies are in this country as envoys on behalf of the Irish Free State. I take this opportunity to inform you that this statement is not correct and that Countess Markievicz and Miss Barry came to this country as envoys of the Irish Republican party, to appeal to Americans for their support in our struggle to maintain the republic established by the Irish people people in elections of 1918. 

THOMAS D. O'CONNOR. 

Secretary. American Delegation; Republican party of Ireland. 
New York, April 18 — Knickerbocker Press, 20 April 1922

A few weeks later, in New York on 18 May 1922, O’Connor was married to Frances Mangan (b. 29 September 1899 in New York); officially emigrating in 1924 and becoming a US citizen several years later, Thomas and Frances raised a family together, having two sons and two daughters. In later life he worked as an accountant for a brokerage firm.

Thomas O’Connor died in New York on 6 January 1955 and was interred in Gate of Heaven Cemetery.