He was also an elected member of the New South Wales Legislative Assembly for one term from 1856 to 1858.
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.
[2] Barker was an appointed member of the Legislative Council between 1853 and 1856, prior to the establishment of responsible government.
[5] He served without distinction in the first responsible parliament and was defeated at the 1858 election with 275 votes (39.29%).
In January 1855 the company, with its line to Goulburn, was acquired by the NSW government and Barker was appointed Commissioner of Railways.