Alfred Bennett Harbage, who would adopt the name Thomas Kyd for his detective writings in middle age, was born in Philadelphia on July 18, 1901, the son of John Albert Harbage, a grocer, and Elizabeth (Young) Harbage. Entering the University of Pennsylvania in 1920, he earned successively the degrees of bachelor of arts (1924), master of arts (1926), and doctor of philosophy (1929). He married Eliza Finnesey in 1926; the couple subsequently had four children.
An academic to the core, he began teaching at his alma mater while a graduate student in 1924 and remained there for twenty-three years, meanwhile earning a reputation as an author of scholarly books on English drama. In 1946 he published the first Phelan novel; the second followed the next year, when he also accepted an appointment as an associate professor of English at Columbia University. After his third Phelan novel in 1948, Harbage turned his attention to the mystery thriller for a time.
With his detective novels behind him, he became professor of English literature at Harvard University in 1952, remaining there until his retirement in 1970 and adding to his already impressive academic achievements. He served as general editor of the thirty-eight-volume Pelican Shakespeare series (1956-1967) and wrote several books on William Shakespeare and numerous scholarly articles. He received many academic awards, including honorary doctorates from the University of Pennsylvania in 1954 and Bowdoin College in 1972.
In retirement Harbage returned to the Philadelphia area where he had spent his first forty-six years, residing in Cherry Hill, New Jersey, until his death at the Pennsylvania Hospital in Philadelphia on May 2, 1976.