[2] During the Second World War, O'Reilly served with the British Army's Royal Engineers from 1943 to 1946, part of which he spent with the 7th Indian Infantry Division during the liberation of Burma from Imperial Japanese occupation in 1944–45.
[2] By the 1960s, O'Reilly was joint managing director of Powers with his cousin John A. Ryan, but whiskey sales were still in decline.
Powers, which had acquired Tullamore in the 1950s, merged with rivals Cork and Jameson to form Irish Distillers, Ltd. (IDL) in 1966, with O'Reilly serving as its first chairman.
In particular, O'Reilly was instrumental in selling IDL to the French company Pernod Ricard in 1988, avoiding a hostile takeover by the UK's Grand Metropolitan group.
[2] In 2002, O'Reilly was invested as a Knight Commander of the Equestrian Order of St Gregory the Great by Pope John Paul II in recognition of his outstanding contribution to the restoration of the Irish College in Paris.