He stood as a Labour candidate, and was elected as the Member of Parliament for Islington North at a by-election in 1969 following the death of sitting MP Gerry Reynolds.
His selection over Keith Kyle was the subject of an investigation in the early 1970s by The Sunday Times newspaper.
[3] His office was invaded by activists in 1977, and he claims that he was punched to the ground and kicked, and was only revived when the police arrived.
[3] During the same year, when the Labour Government's parliamentary majority was under threat, he threatened to resign unless the left wing in his constituency party was brought under control.
The official Labour Party candidate and future leader, Jeremy Corbyn won the seat; whilst O'Halloran came in fourth place with 11% of the vote.