He was born in Kilrush, County Clare and educated at St Flannan's College in Ennis, at University College Galway, and at University College Dublin (UCD) where he received a doctorate in veterinary medicine. He then worked as a lecturer.
Upton was first elected to public office as a Labour Party member of Dublin County Council for Terenure at the 1991 local elections, where he served until the Council's abolition in 1994, and then as a member of South Dublin County Council until 1999.
He had unsuccessfully contested the Dublin South–Central constituency at the 1989 general election. However, he was then elected to the 11th Seanad on the Agricultural Panel, and became the Labour Party's leader in Seanad Éireann.
At the 1992 general election, he stood again in Dublin South–Central, and in Labour's "Spring Tide" surge at that election, Upton topped the poll with nearly 12,000 first-preference votes, a remarkable 1.48 quotas. He was re-elected at the 1997 general election with a considerably reduced vote.
In the 28th Dáil he was appointed as Labour's spokesperson on Justice, Equality and Law Reform. A leading critic of Labour's 1999 merger with the Democratic Left, he nonetheless became the party's spokesman on communications and sport after the merger.
He was a member of the Parliamentary Assembly of the Council of Europe in 1994–95
He died suddenly of a heart attack on 22 February 1999 at the UCD veterinary school, where he was still an occasional lecturer, and was survived by his wife and their four children. Politicians of all parties paid glowing tributes to him an outspoken but "erudite and incisive" contributions to politics and to Irish culture.
Following his death, the University College Dublin branch of the Labour party was named in his honour due to his involvement with the college. It has since been renamed to honour the Spanish Civil War veteran Charlie Donnelly.
- "Dr. Pat Upton". Oireachtas Members Database. Retrieved 14 August 2013.
- "General election 1989, Dublin South–Central". ElectionsIreland.org. Retrieved 5 March 2009.
- "Pat Upton". ElectionsIreland.org. Retrieved 14 August 2013.
- "General election 1992, Dublin South–Central". ElectionsIreland.org. Retrieved 5 March 2009.
- "General election 1997, Dublin South–Central". ElectionsIreland.org. Retrieved 5 March 2009.
- "Politicians pay tribute to `courageous' Upton". Irish Independent. 23 February 1999.
- "Labour TD Pat Upton dies of heart attack". RTÉ News. 22 February 1999. Retrieved 5 March 2009.
- "Colleagues and constituents mourn Labour's Pat Upton". Irish Independent. 25 February 1999.
- "Dublin South–Central by-election, 1999". ElectionsIreland.org. Retrieved 5 March 2009.