Lawyer, statesman and notable Covenanter. Born in Edinburgh, Johnston was educated at the University of Glasgow and admitted to the Faculty of Advocates in 1633. His home was at Warriston near Currie. In 1638, he worked with Alexander Henderson (1583 - 1646) to draft the National Covenant, which denounced attempts by King Charles I (1600-49) to impose Anglican forms of worship on the Scottish church. He was briefly reconciled with Charles, who knighted him in 1641 as part of his attempt to placate the Covenanters. He was also appointed a Lord of Session, as Lord Warriston, and was made Lord Advocate in 1646. Yet, in 1643 he was a prominent member of the Westminster Assembly and by the following year he helped coordinate joint military operations between the Scottish Covenanting and English Parliamentary armies against the Royalist forces of Charles.
In 1647, Johnston continued to lead the radical Covenanters (or Kirk Party) who opposed an alliance with Charles, however when Oliver Cromwell (1599 - 1654) executed the King, Johnston reluctantly backed King Charles II (1630-85). Johnston had been prominent in negotiating the Treaty of Breda in 1650, which imposed significant conditions on Charles in exchange for Scottish support, including accepting that the Presbyterian system of church governance could continue in Scotland. Thus, when Cromwell marched into Scotland in 1651, Johnston lost his offices. However, in 1657, he was appointed Lord Clerk Register and Commissioner for the Administration of Justice in Scotland.
His inconsistent loyalty worked against him and, following the Restoration, he was charged with treason, held in the Tower of London and eventually brought back to Edinburgh where he was hanged.
