Lettice Marston was born on 12 March 1919. At the time of the Munich Agreement in 1938 she joined the City of London Company of the ATS [the women's Auxiliary Territorial Service], quickly becoming Company then Regimental Sergeant Major. She was then commissioned and in 1945 was specially selected to go to Berlin [Germany] as a member of the planning staff making arrangements for the Potsdam Conference on the post-war future of Europe. Marston was the first woman in this position, and while working at the Potsdam Conference [codenamed 'Terminal'] with the Soviet delegation, she came to the attention of General Sir Hastings Ismay, who had been Churchill's Chief of Staff during the war, and now recommended her to Churchill as a personal secretary. Marston was to work for Churchill from March 1946 until his death in 1965, particularly running his constituency affairs and the secretarial side of work on Churchill's war memoirs.

In 1953 she married Robert Shillingford, whom she had met while he was Adjutant of 615 Squadron at Biggin Hill, Kent. Lettice Shillingford died in 1988.