Thomas Barker (25 March 1799 – 12 March 1875) was an Australian businessman and politician who was an integral proponent of many of Sydney's earliest business, educational and political institutions. In his later years he was an appointed member of the New South Wales Legislative Council between 1853 and 1856. He was also an elected member of the New South Wales Legislative Assembly for one term from 1856 to 1858.

Barker was born in London, a son of Mary Shuldham^[1] and James Barker (who died in 1808) and from age nine was raised by a guardian. He was educated at home^{[lower-alpha 1]} and apprenticed to an engineer, John Dickson. Barker accompanied Dickson when he migrated to Australia in 1813 and with Dickson and his brother, James Barker, he built a number of steam driven flour mills.^{[lower-alpha 2]} He made a substantial fortune in the flour milling business and also constructed cotton and woollen mills. He invested in land in the Goulburn Plains district, an estate in Bringelly, and in 1833 he bought 16 acres (6.4 hectares) at Darling Point where he built the palatial Roslyn Hall, designed by Ambrose Hallan, where Roslyn Street, Rushcutters Bay, is today. This was one of Sydney's largest personal residences until it was demolished in 1937. He also invested in the Commercial Banking Company of Sydney and major infrastructure projects including the Sydney Railway Company. He was a promoter of Sydney's earliest educational institutions and a benefactor to Sydney Grammar School, Sydney Mechanics' School of Arts and the University of Sydney.^[2]

Barker was an appointed member of the Legislative Council between 1853 and 1856, prior to the establishment of responsible government.^[3][4] At the 1856 election, the first after the granting of responsible government and creation of the Legislative Assembly, he was elected for the seat of Gloucester and Macquarie with 163 votes (37.73%).^[5] He served without distinction in the first responsible parliament and was defeated at the 1858 election with 275 votes (39.29%).^[6] He did not stand for further public office.^[3]

Barker was an early investor in the Sydney Railway Company and from its second AGM served as a director of the company. In January 1855 the company, with its line to Goulburn, was acquired by the NSW government and Barker was appointed Commissioner of Railways.^[1]

In 1824 Barker married Joan Dickson (died 24 December 1851).^[7] They had no children.