He was on the executive of the
Independent Political Labour League (IPLL) in 1906/07. He was on the Advisory Committee of the
Social Democratic Party in 1915–1916.
Local body politics He was a
Wellington City Councillor from 1919–1925 and 1929–1941, and also served on the Wellington Hospital Board. Chapman served three separate terms on the
Wellington Harbour Board from 1919–21, 1925–31 and 1933–41. In
1915, Chapman ran for
Mayor of Wellington as the Social Democratic candidate. In a three horse race, he came a distant third. He ran for mayor a further three times as the Labour Party's nominee. He ran in
1925,
1927 and
1938 placing second on each occasion. At the
1944 election he was nominated to be Labour's candidate for the mayoralty, one of five candidates he was not selected with Labour Party president
James Roberts prevailing.
Member of Parliament He contested the electorate in the and came third behind
Robert Wright and
William Henry Peter Barber. He contested the electorate in the for the Labour Party and came third behind
Hugh Campbell and
Gilbert McKay. In , he stood in the Hawke's Bay electorate again and came a distant third (and last) after Gilbert McKay and
Andrew Hamilton Russell. In the , he stood in the electorate and was beaten by the incumbent, Robert Wright, who had also beaten him in 1908. In
1928, Chapman was elected as the Member of Parliament for
Wellington North which he held until the seats abolition in 1946. He then became the Member for from
1946 until 1954 when he retired. In 1945 he was appointed a member of the Wellington Rehabilitation Committee. ==Later life==