Cecilia Mary Ady was born at the family home in Edgcote, Northamptonshire, the only child of art historian Julia Cartwright Ady and her husband, the Rev. (William) Henry Ady, an Episcopalian minister. She was educated at home and entered the University of Oxford in 1900. She graduated with a First in the honours school of modern history and travelled in Italy for some time. Following in the footsteps of her mother, she became an art historian and writer. Her first book was A History of Milan under the Sforza (1907), followed by Pius II (Aeneas Silvius Piccolomini): the Humanist Pope (1913). Among her other works were Italy, 1250-1527, which was a chapter in the collection of essays called Italy, Mediaeval and Modern (1917); a translation of History of Modern Italy, 1871-1915 by Benedetto Croce (1929); and Lorenzo dei Medici and Renaissance Italy (1955). In 1909, she became a tutor in modern history at her alma mater, St. Hugh’s Hall. She was named vice principal in 1915 but was dismissed in 1923. The following year, she took a job as tutor to the Society of Home Students, returning to St. Hugh's as a research fellow in 1929. In 1938, she earned a DLitt degree from Oxford. She retired in 1951, when she was elected an Honorary Fellow. She took an active role in church affairs in her diocese and also wrote about the role of women in the church.