Described as a difficult teenager, she attended a number of schools, learning shorthand and typing and working as a secretary at the British legation in Mexico.
She did so and was guided to an office in Whitehall where she was met by a colonel, who had her sign the Official Secrets Act and warned her not to be seen by a certain person standing outside the building when she left.
She was hired by D/MI(R), a section of the War Office concerned, among other things, with disrupting the flow of Romanian oil to the Third Reich.
Subsequently, she became personal assistant to General Sir Hastings Ismay, a close associate of Winston Churchill's.
In 1971, Joan Astley wrote of her wartime life in a memoir, The Inner Circle: a View of War at the Top, and in 1993 co-authored a book on Sir Colin Gubbins.