Mary Kelly was born Mary Theresa Coolican on December 28, 1927, in London, the daughter of Francis Spenser Coolican and Kathleen Reedy Coolican. She was educated at the Ursuline Convent in London and then at the University of Edinburgh, receiving her master’s degree in 1951. In 1950, she married Denis Charles Kelly and moved to Surrey, where she taught in a private school and then in Surrey County Council schools from 1952 to 1954.
Although her first book was published in 1956, it was not until The Spoilt Kill (1961) that critics began to rank her at the top of her genre. For that book she was given the Gold Dagger Award of the Crime Writers’ Association. Between 1962 and 1974, she published six additional novels, and in 1963 American readers discovered her recent books and read her earlier ones. Kelly’s interest in music, particularly in opera, is evident in many of her mysteries.