David Guest (6 January 1911[1]– 28 July 1938) was a British mathematician and philosopher who volunteered to fight for the Republicans in the Spanish Civil War and was killed in Spain in 1938.

[3] There Guest became the head of a party cell that included John Cornford, Guy Burgess, Donald Maclean, Victor Kiernan and James Klugmann.

[6][7] In 1933, after leaving Cambridge Guest moved to Battersea, South London, where he lectured in mathematics and worked for the Communist party at the Peoples' Bookshop in Lavender Hill.

In May 1935, he organised a Youth Peace Parade of fifty young people, some dressed as nurses, others with gas masks and with stretchers, to warn of war.

For a short period of time he taught at a secondary school for English-speaking children in Moscow, but returned to England to lecture at University College in Southampton.