[2] When he was 17, his father had him inducted into the IRB at the side door of a pub by a man who seemed to view the ritual as an unpleasant distraction to a night of drinking.

[3] The event disillusioned McCullough with the IRB, and he took it upon himself to revitalise the organisation, with assistance from, among others, Bulmer Hobson and Seán Mac Diarmada.

It is likely that the other members of the three man IRB executive, Clarke and MacDermott (the treasurer and secretary) supported his nomination as president because, as he was isolated in Belfast, he would be in no position to interfere with their plans.

[6] McCullough stated in his application for an Irish military pension in 1937 that, 'I brought out my men in Belfast and mobilised them at Coalisland to cooperate with the Tyrone Volunteers in accordance with orders from Pearse and Connolly received by me.

He was an ordinary volunteer in the Irish War of Independence (1919–1921), during which he was arrested and imprisoned by the British several times and held for long periods.

[12] In 1922, he supported the Anglo-Irish Treaty, despite its acceptance of the Partition of Ireland, as a way of keeping the republican movement united and focused on the north.

[14] After the Treaty, in early 1922 he was sent by George Gavan Duffy to the United States to make contact with Irish republican organisations there.

McCullough's political activity went alongside maintaining and developing an instrument making and retail music business in Belfast's Howard Street, generated from his original trade as a piano tuner.

In time, after he moved to Dublin, this became McCullough Pigott of Suffolk Street and marked the beginning of a highly successful and influential Free State business career.

While in the U.S. as Special Commissioner for the Free State (leaving his wife in charge of the music business), McCullough's new premises in Dawson Street were destroyed by an Anti-Treaty IRA land mine as a reprisal during the Irish Civil War.