In 1902, he was elected to the Victorian Legislative Assembly for the seat of Villiers and Heytesbury[6] on a platform of "assisting in every practicable way the interests of the dairyman, the agriculturalist and the pastoralist" alongside support for the economic reforms of the Irvine government.[7][8] However, he resigned his state seat, which was about to be abolished in a redistribution, in November 1903 and successfully transferred to federal politics, winning the Australian House of Representatives seat of Corangamite as a member of the Free Trade Party.[9]
In federal parliament, Gratton Wilson described himself as a protectionist but opposed the Protectionist Party due to his hostility towards their more positive relationship with the Labor Party.[10] He thus went into Opposition to Alfred Deakin, but voted against free trade policies.[11] His maiden speech, in March 1904, opposed proposals to increase House sitting days as it would be "too great a tax on businessmen's time".[12][13] He was re-elected in 1906 but was defeated in 1910 by future LaborPrime MinisterJames Scullin.[1][2] He attributed his defeat to "apathy and treachery" by anti-Labor supporters who thought he would win and did not assist him in the face of a strong Labor campaign and "misrepresentations and misunderstandings".[14]
He served in World War I from 1916 to 1919 as a member of the Army Medical Corps, after which he returned to his Warrnambool medical practice and farm. He retired in 1920 and later moved to "Iluka" at Moonlight Head (later Yuulong) near Cape Otway. His Yuulong home was destroyed in bushfires in 1934, though he was still residing in the area in 1939 when he made a donation of 375 ferns to the Wombat Hill Botanic Gardens.[15] He died at Colac, Victoria in 1948, aged 85.[1][2][16][6]