John Brown Watt (16 May 1826 – 28 September 1897) was an Australian politician, Member of the New South Wales Legislative Council.
Watt was born in Edinburgh, Mid-Lothian, Scotland, the eldest son of Alexander Hamilton Watt and his wife Margaret, née Gilchrist. Watt was educated at the University of Edinburgh, matriculating in 1840; he emigrated for health reasons, arriving in Sydney in the Benares on 6 December 1842.
Watt was appointed a member of the Legislative Council of New South Wales in September 1861, but resigned on leaving for England in March 1866. He was reappointed in October 1874. In 1877 he presented the sum of £1000 to the University of Sydney to found an exhibition for students from primary schools. In April 1890 his seat in the Legislative Council became vacant owing to prolonged absence in England.
Watt died in Bournemouth, Dorset, England on 28 September 1897. He was survived by three of his five sons and five daughters, the youngest son was Oswald Watt, aviator.