Presbyterian minister and theological scholar who led the movement in Scotland to reject (1637) the Church of England's Book of Common Prayer. He was a member of the Glasgow Assembly (1638), at which the Church of Scotland broke away from English episcopacy. Baillie became professor of divinity at Glasgow (1642) and in 1661 was made principal of the university. His Letters and Journals, edited by D. Laing (1841–42), are of considerable historical importance.

Scottish Presbyterian executed for allegedly conspiring to assassinate King Charles II of Great Britain. The evidence against him was inconclusive, and Scottish nationalist sentiment has regarded him as a martyr for the cause of religious liberty.

By 1676 Baillie had become involved in the struggle to free Scottish Presbyterianism from domination by the Anglican Church of England. Frustrated in these efforts, he planned to emigrate to South Carolina in 1683, but the scheme fell through. Baillie then travelled to London and met a group of Charles II's political opponents, headed by James Scott, duke of Monmouth, and Lord William Russell. Implicated with these men in the alleged Rye House Plot to murder Charles and his brother James, duke of York (later King James II), Baillie was arrested, imprisoned in London for six months, and then sent to Edinburgh. There he was found guilty of treason and hanged and drawn and quartered.