By his own account, he was one of a number of dock labourers who met one evening in August 1911 at Cromwell's Fort, near Renmore, to discuss the establishment of a union to represent general workers.
Over the following days, news of the al fresco discussion spread around Galway, and a considerable crowd attended a subsequent public meeting at the Racquet Court Theatre.
At that meeting, the Galway Workers' and General Labourers' Union (GWGLU) was established and O'Halloran was elected as its first secretary.
O'Halloran remained as branch secretary, and he would lead his members into a general strike in late March 1913 which shut down the city for five weeks.
Having energetically raised labour matters and actively opposed recruitment into the British army early in World War One, O'Halloran sank into obscurity after 1915.