Notable as a Roman Catholic theologian and a longtime professor at The Catholic University of America's Pontifical John Paul II Institute for Studies on Marriage and Family, he published Catholic Sexual Ethics (1998), Catholic Bioethics and the Gift of Human Life (2000) and Marriage: The Rock on Which the Family Is Built (1995).
At age nine, he decided to become a Catholic priest; however, while studying theology and philosophy at The Catholic University of America, he developed an epilepsy-like condition that he viewed as a sign that he should abandon his quest for the priesthood.
He received the Fellowship of Catholic Scholars' 1979 Cardinal Wright Award and the Center for Bioethics and Culture's 2007 Paul Ramsey Award.
One of three children born to Catholic mother Katherine Armstrong and Presbyterian father Robert May, he spent his youth in St. Louis, Missouri, and was raised in his mother's faith. His marriage to Patricia Ann Keck began in 1958 and produced seven children.
He and Scott Hahn both published works of Roman Catholic religious scholarship.