The former Irish secretary of the Amalgamated Transport and General Workers' Union collapsed and died at the union's annual conference yesterday. Mr Matt Merrigan died after collapsing during the lunch break.
He was the senior officer of the ATGWU in Ireland from 1960 to 1986. He served as president of the Irish Congress of Trade Unions in 1986.
He was a leading figure in the Labour Party as well as the trade union movement and came within 300 votes of winning a Dail seat in 1969.
He helped form the Liaison of the Left in the 1970s and was one of the main opponents of Labour's participation in coalition governments. When Labour entered coalition with Fine Gael in 1973 Mr Merrigan left and became a founder member of the short-lived Socialist Labour Party with Dr Noel Browne.
The Taoiseach offered his condolences to Mr Merrigan's family.
"Matt Merrigan was fervently committed through his long and distinguished career to the wellbeing of the poorer and more marginalised people within Irish society," Mr Ahern said.
Mr Merrigan would have been 79 next week. His wife, Rose, died three years ago. He leaves a daughter, Olga, and a son, Matt.