His was a prosperous upper middle class Anglican family near Nottingham, with an industrial background in the Midlands and earlier aristocratic roots in Scotland. His uncle and godfather was Randall Davidson, the Archbishop of Canterbury (1903 - 1928) and he was the cousin of the writer Sir Walter Scott. He was educated at Winchester College, and New College, Oxford. He was an accomplished flautist playing regularly with the professional London orchestras. He was later much involved in musical collaboration as a librettist, writing song cycles with Benjamin Britten, Alan Bush, Alan Rawsthorne, and Constant Lambert. Among several notable pieces, Swingler co-wrote Ballad Of Heroes with Britten and the poet W. H. Auden and wrote a new version of the English lyrics of the Polish revolutionary song Whirlwinds of Danger.
He joined the Communist Party of Great Britain in 1934. His numerous ventures as a literary entrepreneur included: the setting up of Fore Publications (1938); the magazines Left Review (to 1938), Arena, Seven (taken over in wartime, mainly for the paper stock), Our Time; and the publishing of the Key Books, and later Key Poets series. These proved more influential than his Blake-flavoured verse, which has consistently been criticised (and scarcely defended, except by Andy Croft).
He operated in North London, as a close associate of Nancy Cunard, sometimes lending his name. He was one of the organisers of the covert Writer's Group of the late 1930s, attempting to co-ordinate a 'literary policy' of the Left. He was involved also in work for the Unity Theatre. He was the literary editor of the Daily Worker, and often reviewed books for The Times, The Manchester Guardian, and other newspapers. With his brother, the Labour MP Stephen Swingler, he was involved in Barnett Stross's Lidice Shall Live campaign. He wrote the words to the piece A Rose For Lidice (music by Alan Rawsthorne) which was performed at the opening of the memorial rose garden in Lidice in 1955.
He served with the British Army in Italy in World War II. His egalitarian beliefs led him to refuse a commission and he joined as a private soldier, repeatedly refusing offers of a battlefield commission. He saw action in the Italian campaign and was awarded the Military Medal. He left the CPGB in 1956. He was a founder of E. P. Thompson's The New Reasoner (from 1957).
- Crucifixus (1932) play
- Difficult Morning (1933) poems
- The Left Song Book, (1938) compiled with Alan Bush
- The Years of Anger - poems
- The God in the Cave (1950) poems
- Selected Poems of Randall Swingler (2000) edited by Andy Croft
- Comrade Heart: A Life of Randall Swingler (2003) by Andy Croft