Kathleen O'Shea was born in Oklahoma City, Oklahoma, in November 26, 1944. She was adopted in infancy by Sarah Alida Conde O'Shea and James O'Shea and grew up in Salina, Kansas. In eighth grade she decided to become a nun in the Catholic Church. In 1958 she became an Aspirant of the Apostolic School at Nazareth Motherhouse in Concordia, Kansas, but was sent home at the end of the year to wait until she was "more mature." In 1960, O'Shea began her Postulancy at St. Joseph's Villa in Peapack, New Jersey, graduating in 1962. She entered the Immaculate Heart Novitiate in Glen Cove, New York in August, 1961, and became a nun (Sister Mary Fidelis) in 1963. O'Shea was a nun for 30 years, after which she began work as social worker doing research on female offenders, with an emphasis on women on death row. She is the author of Female Offenders: An Annotated Bibliography (1997), Women and the Death Penalty in the United States: 1900-1998 (1999), and Women on the Row: Revelations From Both Sides of the Bars (2000), which was nominated for a Pulitzer.