 He was first elected to the House of Commons as Member of Parliament (MP) for Lewisham North, at a by-election in 1957 following the death of Conservative MP Sir Austin Hudson.MacDermot lost his seat two years later at the 1959 general election, and unsuccessfully contested the equivalent seat at the 1961 London County Council election.He returned to Parliament as MP for Derby North at a by-election in 1962.