At various times he was General Secretary of the Labour Party, a Teachta Dála (TD), a Senator, and a Member of the European Parliament (MEP).

He strongly supported both approaches, but was instrumental in securing the party's eventual, somewhat unwilling, reversal of its anti-coalition stance after its disappointing result in the 1969 general election.

[5] He continued to serve as General Secretary of the party until 1980, and was appointed a Member of the European Parliament (MEP) from 1983 until 1984, replacing Frank Cluskey, where he specialised in economic affairs and energy policy.

[citation needed] In 1980, Halligan set up CIPA, his own public affairs consultancy based in Dublin, and became a lecturer in Economics at the University of Limerick.

[6] In 1985, he was appointed as Chairman of Bórd na Móna, the Irish Peat Development Authority, a position he held for ten years.

[9] In later years he also worked on the foundation and development of the Ireland China Institute (ICI), which, with its maxim bridging the gap between knowledge and understanding, seeks to strengthen Irish-Chinese diplomatic relations, developing cultural links and fostering a deeper understanding of the respective cultural norms and values between the two nations.

On his death, Taoiseach Mícheál Martin described him as “a man who gave his life to politics and the public service with a deep commitment to the institutions of the state”.