Author R. M. Douglas wrote that Treacy was a party member of fringe Fascist group Ailtirí na hAiséirghe during the 1940s.[5] However, by the 1960s Treacy had moved to the ideological left, albeit he was still considered to be socially conservative.[2] Treacy was first elected to the Dáil at the 1961 general election, as a Labour PartyTD for the Tipperary South constituency. He was re-elected there in seven subsequent elections, and returned automatically in three more owing to his having been elected by the Dáil as Ceann Comhairle. He was elected to that office first after the 1973 general election for one term, then after the 1987 general election for three.[4] As Ceann Comhairle, he was a member of the Irish Presidential Commission during the presidential vacancies of 1974 and 1976.
He was expelled from the Labour Party in 1985 for voting against the family planning bill, which would have liberalised the sale of contraception in the Republic of Ireland. He was elected as an Independent TD at the 1987 general election.[6] After that election, he was elected as Ceann Comhairle by the Dáil. One of his first acts was to exercise his casting vote in favour of the nomination of Charles Haughey as Taoiseach.[7] Treacy retired from politics at the 1997 general election, the only Ceann Comhairle to retire from the position at an election, rather than exercising his right of automatic re-election.[8]
^ ab"Seán Treacy". Oireachtas Members Database. Retrieved 18 March 2009.
^Douglas, R. M. (2009). Architects of the Resurrection: Ailtirí na hAiséirghe and the Fascist 'New Order' in Ireland. Manchester University Press. p. 250. ISBN978-0-7190-7998-6.
^Treacy served as Ceann Comhairle in the 20th Dáil from 1973 to 1977, and was returned automatically at the 1977 election. He lost the Labour party whip in February 1985.
^Treacy served as Ceann Comhairle in the 25th, 26th and 27th Dáil from 1987 to 1997, and was returned automatically at the 1989 and 1992 elections.
