Thomas Robert Dewar was born at Perth on 6 January 1864 and became a whisky blender and politician. One of the most successful whisky blenders businesses was John Dewar & Sons Ltd of Perth. John Alexander Dewar and Thomas Robert Dewar joined the firm in 1879 and 1881 respectively. After 1881, John Alexander and Thomas Dewar, developed their product into a household name.
Thomas Dewar was active in civic and political life in London: he served on the London county council for West Marylebone from 1892 to 1895, and was Conservative MP for the St George's division of Tower Hamlets in London from 1900 to 1906. He became lieutenant of the City of London.
Knighted in 1902, Dewar received a baronetcy in 1917, and was created Baron Dewar of Homestall in 1919. Dewar's interests included painting, shooting, racing, and coursing. Lord Dewar died on 11 April 1930 at his Sussex home, The Homestall, East Grinstead.