Harry was the ninth and youngest child of William Clark and Marianne (nee Newport). He grew up in Ampertaine, a fine Georgian house which reflected the tastes of his mother’s Waterford family. A strong and rambunctious character, he left Coleraine Academical Institution at the age of 15 and joined the family linen business which was already 150 years old. Starting young was a family tradition: his brother Alexander had begun making successful calls on customers in Glasgow when he was 17.
In 1888, Harry felt the business was too small to support two brothers, so he decided to sail away to some distant land. His family managed to intercept him at the dockside and made a counter-offer. He could travel as a salesman for the family enterprise. This led to the first of many brilliant sales trips to the United States, Canada and beyond. Aged 19, he hired and fired agents, befriended an Indian chief near Montreal and met President Cleveland at a White House reception. Everywhere, he used Irish connections.
In 1896, soon after building Ardtara, he married Alice Warren Moore, a 17-year-old beauty, and they had six children: William (1897), Tom (1898), Norah (1900), Harry (1904), Brian (1907) and Mamie (1909). Soon after Harry’s marriage, the business became a limited company owned by Alexander, Harry and their father William.
Between 1888 and 1914, annual turnover rose from £40,000 to about £400,000.
In due course, Ardtara became a beloved family home for nine grandsons and two grand-daughters.
Harry’s passions included motoring, fishing and rough-shooting. He encouraged his children, nephews and nieces to travel far afield and rejoiced in their achievements. He was an enthusiastic diary-keeper and a good amateur historian. When Harry's grandson Wallace Clark wrote "Linen on the Green" - a history of Upperlands - he drew heavily on Harry's diaries as well as the memoirs of his great-uncle Percy Clark.