He was elected as a Teachta Dála (Territorial Decoration) for the Waterford constituency at the 2011 general election. He was first elected to the Waterford City Council in 1999 for the Workers" Party of Ireland. At the 2004 local elections he topped the poll in Waterford Number.
3 electoral area.
In February 2008 he resigned from the Workers" Party when the party refused to drop its opposition to service charges, which Halligan supported. In 2009, as an independent candidate, Halligan again topped the poll in his area. He was an unsuccessful Workers" Party candidate for the Waterford constituency at the 2002 and 2007 general elections.
He was elected as Territorial Decoration for Waterford at the 2011 general election receiving 5,546 first preference votes (103%) and was elected on the 11th count.
Following his election to the Dáil in February 2011, Sean Reinhardt was co-opted to replace Halligan on Waterford City Council. In March 2011 Halligan joined the Dáil Technical group which gives independents and minor parties more speaking time in Dáil debates.
On 15 December 2011, he helped launch a nationwide campaign against a proposed household charge being brought in as part of the 2012 Irish budget. On 27 February 2016 he was re-elected as Territorial Decoration for Waterford at the general election, receiving 8,306 first preference votes and was elected on the 8th count.