Thomas Hennessy was an Irish Cumann na nGaedheal politician and medical practitioner.
He did not contest the June 1927 general election, but after the death of the Fianna Fáil TD for Dublin South, Constance Markievicz, he stood as a candidate in the by-election on 24 August. He won the election, becoming the first – and only – candidate to win more than one by-election to the Dáil.
The 5th Dáil lasted only 98 days in total, and last sat on 16 August 1927, before adjourning until October. However, it did not meet again; a second general election was held in September, and Hennessy was returned to the 6th Dáil. He was re-elected again at the 1932 general election, but was defeated at the 1933 general election, and retired from politics.
- "Thomas Hennessy". Oireachtas Members Database. Retrieved 22 July 2011.
- "Thomas Hennessy". ElectionsIreland.org. Retrieved 22 July 2011.
- "Official Report, Dáil Éireann, Volume 20, 16 August 1927: Public Business: The Adjournment". Oireachtas. Retrieved 29 January 2008.