In 1976, aged 22, O'Callaghan ended his involvement with the IRA after becoming disillusioned with its activities. He later recalled that his disenchantment with the IRA began when one of his compatriots openly hoped that a female police officer who had been blown up by an IRA bomb had been pregnant so they could get "two for the price of one." He was also concerned with what he perceived was an undercurrent of ethnic hatred in its rank and file towards the Ulster Scots population. He left Ireland and moved to London. In May 1978, he married a Scottish woman of Protestant unionist descent. During the late 1970s, he ran a successful mobile cleaning business. However, he was unable to fully settle in his new life, later recalling: "In truth there seemed to be no escaping from Ireland. At the strangest of times I would find myself reliving the events of my years in the IRA. As the years went on, I came to believe that the Provisional IRA was the greatest enemy of democracy and decency in Ireland".