Thomas Clarke was a member of the IRB (Irish Republican Brotherhood forerunner to the IRA) when he was 18 years old. He was the eldest member of the Rising and the first signatory of the Proclamation. Patrick Pearse felt that for all Clarke went through (spending 15 years in prison of a life sentence), Clarke should be the first to sign the Proclamation.
Thomas was stationed at the GPO during the Rising. Thomas Clarke was a mentor to Sean McDermott. Both were executed after they surrendered to the British Army under General Maxwell.
- Thomas Clarke Tower in Ballymun was named after him. The top floor was used as a short stay hotel before its demolition in April 2008.
- Dundalk railway station was given the name Clarke on 10 April 1966 in commemoration of Clarke's role in the 1916 Rising.
- He is also featured on postage stamps in 1966.
- Dungannon Thomas Clarkes, a successful Gaelic Football team from East Tyrone in the North of Ireland, are also named after him.