She was born Kathleen Corrigan into a large Liverpool family, and developed a talent as an organist. In 1933, she entered Stanbrook Abbey in Worcestershire as a nun, and eventually became director of its choir. One of her projects was to develop an English language version of the office of Compline for the abbey. In the course of her career, Dame Felicitas befriended and/or corresponded with several famous figures who converted to Catholicism, including poet Siegfried Sassoon, actor Alec Guinness; and novelist Rumer Godden.
Dame Felicitas' biography of Helen Waddell was awarded the 1986 James Tait Black Memorial Prize. Her book, The Nun, the Infidel, and the Superman, inspired by the life of Laurentia McLachlan, was turned into a play by Hugh Whitemore and later became a film for television starring Wendy Hiller. She also wrote about other figures in whom she was interested, including Hildegard of Bingen and the poet Coventry Patmore. She also edited publications for the Stanbrook Abbey Press. Other works include:
- In a Great Tradition (1956)
- George Thomas of Soho (1970)
- Siegfried Sassoon: Poet's Pilgrimage (1973)
- Benedictine Tapestry (1991)
Dame Felicitas was Stanbrook Abbey's organist from 1933 until 1990. She died at Cheltenham.