He was elected as MP for Chelmsford at a by-election in April 1945, for the short-lived Common Wealth Party. The vacancy was created by the death of the previous Conservative member, Colonel John Macnamara, killed on active service in Italy. Whereas the Conservative, Liberal and Labour parties had agreed an electoral truce, the Common Wealth Party refused to accept this. The local CW Party had six members and soon raised £200 for the electoral campaign. After a brief discussion the localCommunist Party decided not to support him. Nevertheless, he received the support of much of the labour movements as he advocated a distinctly socialist programme. Millington wore his DFC ribbon on his uniform when attending the House of Commons, as was customary at the time. Many years later he fondly recalled being reprimanded by a Conservative MP who bemoaned the fact that Millington's ribbon was being incorrectly worn. Millington told the BBC, "I was approached by a Tory MP dressed in civilian clothes and with a hand in his trouser pocket. 'Your DFC ribbon is worn too wide'. He was, I think, not expecting my reaction. 'If you are talking to me as an RAF officer: stand to attention; take your hand out of your trouser pocket and address a senior officer as Sir. If you are talking to me as a fellow Member of Parliament, mind your business and bugger off.'" Millington saw himself "as a communist with a small c", and advocated a socialist program based on nationalisation of the land and public ownership. At the by-election he overturned a Conservative majority of 16,624 to win by 6,431 votes, becoming the Baby of the House. He was one of the first public figures to question the morality of the area bombardment of Germany. Millington held his seat in the 1945 general election and joined the Labour Party in April 1946. He lost his seat in the 1950 general election.
Later life
Millington rejoined the RAF in 1954, but later embarked on a career in education, becoming the Head of Education at ShoreditchComprehensive School in 1965. He later retired to France, where he lived until his death. Millington and his second wife emigrated to France in the early 1980s. Millington's autobiography, Was That Really Me?, was published in 2006. Millington is survived by his four daughters, all of whom were by his first wife, who died in 1979.