 He was one of the foundation members of the Ipswich Oddfellows' Lodge and was a member of the Ipswich Masonic Lodge.In 1906, he was elected to the Australian House of Representatives as the Anti-Socialist member for Moreton.After the "fusion" of 1909, Sinclair, together with the rest of the Anti-Socialists, merged with the Protectionist Party to form the Commonwealth Liberal Party, which in turn merged into the Nationalist Party in 1917.