He was also instrumental in disrupting competition by John Jacob Astor's Pacific Fur Company. Stuart became a partner in the North West Company in 1813 and a Chief factor in the Hudson's Bay Company after its merger with the North West Company in 1821. Stuart is noted for his exploration of Fraser Lake, where he and Fraser built a post, now known as Fort Fraser. Stuart Lake and Stuart River, both in British Columbia are named after him. According to Father Adrien-Gabriel Morice, a missionary and historian of northern British Columbia, Stuart "seems to have been one of those well-meaning men who, unconscious of their own idiosyncrasies, make life a burden to others". At Stuart's initiative, his nephew Donald Smith (later Baron Mt. Royal and Strathcona) was persuaded to come to Canada, where he would play an instrumental role in the building of the Canadian Pacific Railway. John Stuart returned to Scotland in 1836 and died on 14 January 1847, at Springfield House, near Elgin. He married Catherine Lavalle and had two sons. He also had a daughter Isabel in 1802 whose mother is unknown. In 1827 John Stuart took another country wife, Mary Taylor born 1796. She joined him in Scotland in 1836 but because he withdrew his promise to marry her formally she returned to Rupert's Land in 1838. There was considerable litigation over Stuart's legacy to her, which Stuart's sisters managed to have reduced from L 500 to L350. All of his children were born in Canada and it is believed they remained there after his departure for Scotland.