Carlaw joined the East Renfrewshire Conservatives in 1978. He was the Conservative candidate in the 1982 Queen's Park by-election, and in the 1983 general election in Glasgow Pollok. He was Chairman of the Scottish Young Conservatives from 1984 to 1986, Chairman of Eastwood Conservatives from 1988 to 1992, and was Deputy Chairman of the Scottish Conservatives from 1992 to 1998.