[2] After studying at Glasgow University he was appointed by his uncle, James Hamilton, 1st Viscount Claneboye as land agent, overseer and general manager of his estates in Ireland.
He attracted the attention of Robert Blair, at that time minister of the church at Bangor, County Down, who persuaded him to enter the ministry.
In 1626, despite unorthodox views which resembled Blair's own in regard to episcopacy, he was ordained by Bishop Robert Echlin, and presented by Lord Claneboye to the church at Ballywalter in county Down.
Bramhall called a halt, and, having obtained an adjournment, persuaded Leslie not to resume it, but to pass sentence on the recalcitrant ministers.
[3] In September 1636 he and other Scots and English puritans to the number of 140 sailed for New England in a ship called the Eagle Wing, which they had built for the purpose.
On his return to Scotland the ship in which he and several others, including his father-in-law, had taken their passage, was captured by the "Harp", a Wexford frigate, commanded by Alaster MacDonnell, who was bringing reinforcements to James Graham, 1st Marquess of Montrose in the Highlands.
Released on 20 November 1652 on Oliver Cromwell's order, he returned to Edinburgh, where he preached until the restoration of the episcopacy in Scotland which drove him from his pulpit.