Coughlan stood for election as a Clann na Poblachta candidate at the 1954 general election, when he won the second-highest number of first-preference votes, but failed to win enough transfers to secure any of the four seats. He stood again for Clann na Poblachta at the 1957 general election, but his vote had fallen significantly and he was again unsuccessful.
As Clann na Poblachta declined in support in the late 1950s, Coughlan joined the Labour Party and was elected as a Labour candidate at the 1961 general election taking his seat in the 17th Dáil. He was returned to Dáil Éireann at the next three elections, but lost his seat at the 1977 general election to a former Labour party running-mate, Michael Lipper, who stood as an independent.
Coughlan was described by the Irish political magazine Nusight as "personifying a parochialism and prejudice hitherto unknown at a national level". He was known for holding numerous views that conflicted with the Labour Party and his relationship with the Labour Party was always poor, particularly with Barry Desmond. He welcomed the controversial Springbok tour to Limerick in 1970, much to the chagrin of the Labour Party and the local Limerick City Labour chairman Jim Kemmy.
As well as his career in the Dáil, Coughlan was also a long-serving member of Limerick City Council, and was the Mayor of Limerick from 1951–52 and 1969–1970.