G. I. Williamson graduated from Drake University and received the B.D. degree from Pittsburgh-Xenia Theological Seminary. He has served congregations of the old United Presbyterian Church of North America, the Associate Reformed Presbyterian Church, and the Reformed Presbyterian Church of North America, but most of his ministerial labors have been with the Reformed Churches of New Zealand and the Orthodox Presbyterian Church. He is author of popular study guides to the Westminster Confession of Faith, the Shorter Catechism and the Heidelberg Catechism.