After graduating from Dartmouth College in 1960, Turner served a stint in the Army, then worked as an actuary and a car salesman before entering the Union Theological Seminary in Virginia, seeking to become a Presbyterian minister.
Although he earned a master's degree in theology in 1966, he decided against the ministry and instead entered Duke University's religious program, seeking a doctorate in early Christianity.
While at Duke, he joined a team of about 20 young American scholars assembled by James M. Robinson to edit and translate the Nag Hammadi library.
His expertise was in Biblical studies, New Testament, Hellenistic and Graeco-Roman religion and philosophy, Gnosticism, later Platonism and Neoplatonism, Coptic language and literature.
He had expertise in the study of ancient Gnosticism, in particular the restoration, conservation, translation, and interpretation of the thirteen fourth-century papyrus codices from Nag Hammadi.