Sir Thomas was born at Brisbane House near Largs, and succeeded to the Brisbane estate in 1812. In 1819 he married the only daughter of Sir Henry Hay Makdougall, Baronet of Makerstoun, and added Makdougall to his own patronymic when he succeeded to that estate. He entered the army in 1790 and rose to the rank of General, serving on the Continent, the Peninsula, the West Indies, India and America. He went to New South Wales as Governor in 1821. He explored the north of Australia and founded a penal settlement on the River Brisbane which, like the capital of Queensland which appeared later, took its name from him. He was a keen astronomer and in 1822, while in Australia, built the Parramatta Observatory at his own expense. On his return to Scotland he established a meteorological and magnetic observatory at Makerstoun near Kelso where he, with John Allan Broun, did outstanding observational work.