Treadgold was born on 16 April 1910 at 51 Woodberry Crescent, Muswell Hill, north London. Her father John was a stockbroker and a Member of the
London Stock Exchange, and the family was comfortably off. Treadgold attended Ginner-Mawer School of Dance and Drama (1916–22), Challoner's School (1921–1923), and
St Paul's Girls' School, London (1923–1928),
Marcus Crouch described it as "perhaps the most delightful book by a most talented writer" and as making "an effective contribution to the race question because there is no mention of it." Treadgold wrote a trilogy based on a house called The Heron:
The Heron Ride,
Return to the Heron and
Journey from the Heron. The first two volumes were written in the early 1960s, the last in the series was completed in 1981. Treadgold lived in London for most of her life. She died of cancer on 14 May 2005 at St Teresa's Nursing Home in
Kensington, aged 95.{{cite news |author= |title=Death notice |newspaper=The Times ==Selected works==