Described as "a nobleman of impeccable background and proven military ability", he was the only son and heir of Andrew Stewart (d1578), Master of Ochiltree, and Margaret, daughter of his first cousin Henry Stewart, 2nd Lord Methven of Methven Castle. He was the grandson of Andrew Stewart, 2nd Lord Ochiltree, whose title he succeeded to after his father predeceased his grandfather.
He became a General in the Artillery and held the office of General of Edinburgh Castle. Though successful in this campaign, the King had no money with which to reward his military service and instead (in 1609) offered him 3,000 acres of land in County Tyrone, which included the Manors of Castlestewart and later Manor Forward, encompassing the area around Farlough and Roughan, all in the Barony of Dungannon. He was one of the chief "planters" or "undertakers" in the Ulster Plantation and in 1611 he settled on these estates.
He built houses, farmed the land, constructed Roughan Castle and provided housing and employment for the local populace.
He lived at Irry, which was later renamed Stuart Hall by his descendants. As compensation, in 1619, James VI and I raised him to the Peerage of Ireland and created him Baron Castle Stewart.
Number parliament sat between the years of 1615 and 1634, so he never voted. They were the parents of five children:
Sir Andrew Stewart (1590-1639) 1st Baronet & 2nd Baron Castle Stewart.
Married Anne, daughter of John Stewart, 5th Earl of Atholl
John Stewart (d1685), 5th Baron Castle Stewart.
Died unmarried
Colonel Honorary Robert Stewart (1598-1662) of Irry, Company Tyrone; ancestor of the Earls of Castle Stewart
Honorary
Margaret Stewart, married George Crawford of Crawfordsburn, Company
Down
Honorary Maria Stewart, married John Kennedy, ancestor of the Kennedys of Cultra, Company Down
Honorary Anna Stewart, died unmarried.
