First Bethany is the result of the merging of the Bethany Evangelical Church and Zion (First) Reformed Church in 1953. In the merger agreement, it was decided that a "branch church would be developed in one of the east side suburbs". On November 18, 1953, a 2.5-acre site was purchased on Harmon Street, in St Clair Shores. The first phase of the church was constructed in 1955-56 with the inaugural ceremony on Easter Sunday, April 1, 1956. The fellowship hall was added at a later date.

Before the merger of the Evangelical and the Reformed Churches was completed, a further and more inclusive process of union began. In 1937, a study group of the Congregational, Evangelical and Reformed pastors met in St. Louis led by Truman B. Douglass and Samuel D. Press. They explored the possible merger of Congregational Christian Churches (origins in England with the separatist Puritans who migrated under oppression to Plymouth, Massachusetts in 1620) with the Evangelical and Reformed Church. The result was the establishment of the United Church of Christ in 1957. Believing that, in Christ, all the various Christian denominations have more in common than in differences, the United Church adopted the theme "That they may all be one" (quoting Jesus).