Ralph T. Davis attended Moody Bible Institute of Chicago, and there decided to become a missionary. He served in the Army in 1918, and was married the next year, 1919. In 1921 Ralph and Ellen Davis began a career as missionaries in Africa under the sponsorship of Moody Church. The Davises worked principally in the Congo, and also in South and Central Africa, until they returned to the United States in 1935.

Davis then assumed administrative duties with Africa Inland Mission, headquartered in Brooklyn, NY. He began working as a Deputation Secretary in 1936 in the Chicago area, and in 1939 he assumed the post of Assistant General Secretary and served in that capacity until he became General Secretary for the American Home Council in 1941.

In 1950 Wheaton College honored his work with AIM by conferring a Doctorate of Divinity on him. In that same year, Davis began work on a constitutional committee for the mission, which culminated its work with the adoption of a new constitution in 1955. In June of 1955, at the International Conference in Kijabe, Kenya, Dr. Davis was appointed International General Secretary, and remained in this position until he became Director Emeritus in 1962. The Davises moved in that year to Clermont, Florida, where AIM had established a retirement home called Media. Even though in poor health, Davis conducted a voluminous correspondence, edited a monthly pamphlet, "Fuel for Prayer Fires," and continued to accept a limited number of speaking engagements. Davis assumed the interim chairmanship of the complex just before his sudden death on August 19, 1963.

The Davises had one son, Rev. Robert Davis, who in 1962 was director of AIM radio in Kenya, Africa.