He was dissuaded from enlisting immediately in the British army by his parents: his father, also Thomas, had been gassed in the first World War and suffered serious lung problems which led to his early death in 1944.
The young Tom went instead to Queen's University in Belfast to study commerce but, a year later and still uncertain about his long-term plans, he joined the Royal Inniskilling Fusiliers, being commissioned in 1943.
In the post-war period, he was given two years to finish his college course and spent a summer studying law with a tutor before passing the English bar and returning to the British army.
He was offered a job as legal adviser in London to James North Ltd, a company which made protective clothing; with no experience of industry, he asked to be given a managerial role at first.
He slotted easily into the city's old business establishment, joining the Kildare Street club, becoming a director of Pim's department store, and setting his career firmly on a commercial rather than a legal path.
He was asked later by The Irish Times to see if Roy Thomson, the Canadian-born British press baron whom he had met while they both looked separately at the Evening Mail, might be interested in taking it over.
A year later, another problem was resolved when Douglas Gageby, who had been hired as managing director of The Irish Times shortly before McDowell's arrival, took over as editor.
The formation of the trust left the newspaper with a large bank debt, used to buy out the directors/shareholders, at what turned out to be a difficult economic period after the first oil crisis hit the western world in the autumn of 1974.
He stood down as chief executive of the company in 1997 and retired from the chairmanship of The Irish Times Trust in 2001: he was given the title President for Life in recognition of his huge contribution to the newspaper.
During his visit to the new The Irish Times offices on Tara Street, in June 2008 for the unveiling of a portrait of him by Andrew Festing, he described the newspaper and his family as the two loves of his life.