Jennings was nominated to the Legislative Council in 1867. He resigned in 1870 to enter the Legislative Assembly as member for the Murray, but resigned in 1872 and was out of parliament for some years. He unsuccessfully contested the 1874 election for Mudgee, the Upper Hunter by-election in June 1875 and the 1877 election for Wellington. He was a New South Wales Commissioner at the colonial exhibition in Melbourne in 1875, represented the colonies of New South Wales, Queensland and Tasmania, at the Philadelphia exhibition in 1876, executive commissioner for the International Exhibition in Sydney in 1879.