Stewart was a burgess of Edinburgh in 1708, and of Glasgow in 1716. He was a commissioner of supply for Kirkcudbright Stewartry in 1706. He held land both in Livingstone in Kirkcudbright and at Stewartfield in Jedburgh, the first inherited from his father, and the latter through his marriage in 1704 to Elizabeth Scott, the daughter and heir of Sir Francis Scott of Mangerton in Roxburghshire.[2]
Those landholding qualified him as a freeholder, with a vote in each county's elections. After the by-election in Roxburghshire in 1726, a meeting of the county's freeholders was followed by a dinner. One of those present was the by-election winner Sir Gilbert Eliott, 3rd Baronet, of Stobs, who complained to Stewart for not voting for him. An argument followed, and Stewart threw a glass of wine in Eliott's face, who responded by running his sword through the seated Stewart.[3]
Stewart managed to stand and return two blows before the two men were separated, but the wound was fatal. Stewart's dying words were that he had been murdered sitting in his chair, and that his assailant was Sir Gilbert Eliott.[3]
Eliott was declared an outlaw, and escaped into exile before being given a royal pardon.[3]