Born in Brixton, London in 1879 Manson studied at Heatherley School of Fine Art and then at Lambeth School of Art. In 1903 he married the violinist Lilian Beatrice Laugher and moved to the Latin Quarter in Paris. There he shared a studio with Jacob Epstein with whom he studied at the Academie Julian under Jean-Paul Laurens. The following year he returned to Hampstead where he stayed for the next 30 years.
In 1911 Manson became a founder member of the London Group and was one of the exhibitors in the original Camden Town exhibition at the Carfax Gallery in 1911. He later formed the Monarro Group in 1919 with his close friend Lucien Pissarro; the group was aimed at showing artists inspired by Impressionist tradition.
In 1912 he took the job of Clerk at the Tate Gallery, later becoming Assistant Keeper in1917 then Director in 1930, a post he held until 1938. He continued to paint throughout, exhibiting at the New English Art Club from 1915 onwards, becoming a member in 1927. He held his first solo exhibition held at the Leicester Galleries in 1923 and, in 1939, began exhibiting at the Royal Academy.
His reputation as an artist was primarily as a flower painter.