His mother died when he was very young, and the family moved to Melbourne, where he attended Essendon Primary School until the age of 14.
In 1895, Thomson came to Western Australia, working as a journeyman at Fremantle before establishing a business there.
Thomson led the three-member Executive Country Party to the 1924 election, where most of the Majority faction lost their seats.
He stood for and won a by-election for one of the South-East Province seats in the Western Australian Legislative Council on 26 September 1931 following the death of Hector Stewart, which he retained until his retirement at the 1950 Legislative Council election, at which his son, Jack Thomson, succeeded him.
Thomson died at home on 18 November 1953, aged 80, and was cremated at Karrakatta Cemetery.