He was the fourth son of Sir James Steuart of Coltness, a banker in Edinburgh, by Anne Hope, niece of Sir Thomas Hope. He was called to the bar on 20 November 1661, but lost almost all his practice defending his father against a charge of embezzlement.
Stewart found it necessary to leave the country because of a pamphlet, and went to Rouen, where he became a merchant under the name of Graham. Some years afterwards he returned to Scotland, but he was suspected of having had a hand in a further political pamphlet, An Account of Scotlands Grievances by reason of the Duke of Lauderdale"s Ministry (1675), an order was issued for his apprehension. He escaped, and in England under the name of Lawson.
In 1678 Stewart opened a small office in London, where he gave legal advice at half fees, his clerk meeting the clients and transmitting their statements to the invisible Stewart.
Returning to Scotland in 1679, he again got into trouble in 1681, when among the papers of Archibald Campbell, 9th Earl of Argyll a memorandum in his hand was found, reflecting on the government. He took refuge in The Hague.
He was present at the meeting at Amsterdam in 1685, when the expedition of Argyll was resolved on. Stewart having prepared Argyll"s declaration of war, he was accused of treasonably consulting and contriving Argyll"s rebellion, He was found guilty in his absence.
His sentence was to be executed whenever he could be foundation
Stewart was pardoned by James II of Great Britain in 1687, and returned to London. His actions have been interpreted as those of a double agent. In 1692, after the Glorious Revolution, Stewart was appointed Lord Advocate, and during his term of office introduced legal reforms in Scotland.
He resigned office in 1709, and, dying in 1715, was buried in the church of Old Grey Friars.
