She was born Kathleen Corrigan, into a large Liverpool family, and developed a talent as an organist. In 1933 she entered Stanbrook Abbey in Wiltshire, as a nun, and 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, notably the poet Siegfried Sassoon (whose conversion to Catholicism was due in part to her influence), actor Alec Guinness, and novelist Rumer Godden. She wrote a prize-winning biography of Helen Waddell. The Nun, the Infidel, and the Superman, one of the books inspired by her predecessor, Dame Laurentia McLachlan, was turned into a play by Hugh Whitemore and later a film starring Wendy Hiller as Dame Laurentia.
Dame Felicitas 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: