Chetwynde was founded as "Our Lady's Chetwynde School" in 1938 by Sister Aquinas and her nuns as a girls' school. In 1976 the school became mixed and independent from the church, though it retained its Catholic faith and ethos. Under Margaret Stones, the school's first headteacher, Chetwynde achieved high levels of sporting and academic success. The next headteacher was Isobel Nixon; during her time as headmistress the school dropped the "Our Lady's" prefix from its title and the school's record of high academic and extra-curricular achievement was maintained. New laboratories were built with the help of the John Fisher Foundation and many other modernisations took place.