The roots of Simpson University and A.W. Tozer Theological Seminary go back to the founding of Simpson Bible Institute in Seattle in 1921. Started as a training school for missionaries bound for Asia, particularly China and Vietnam, Simpson also became the Bible college for the Christian and Missionary Alliance in the Western United States. In 1955, Simpson College relocated to San Francisco. During the 1970s, graduate degrees were introduced. In 1989, the college relocated to Redding, CA. The Simpson Graduate School of Ministry was launched, offering masters degrees in ministry studies and intercultural studies (missions). Since the mid-1970s, over 350 students have graduated from Simpson Graduate School of Ministry.

In 2006, Simpson University received permission from the family of A.W. Tozer to use his name, and in May 2007 the Graduate School of Ministry was relaunched as A.W. Tozer Theological Seminary.