Gary received his B.A. degree from Concordia Senior College, Fort Wayne, Indiana in 1972. He earned both the M.Div. and the Th.D. degrees at Christ Seminary-Seminex, St. Louis, Missouri. (1976 and 1983).

As of 2015, he is a Professor of Systematic Theology and Northwestern Lutheran Theological Seminary Chair in Theology.

Gary Simpson was named associate professor of systematic theology at Luther Seminary in 1990 and professor of systematic theology in 1998. Earlier, he served as a Lutheran pastor for 14 years.