Grimes Gatlin attended Oklahoma City University, graduating with his B.A. in 1936. He then attended Southern Methodist University, graduating in 1943, and was ordained a Methodist minister. He first served as pastor of Grandview Methodist Church in Grandview, Texas, and then entered military service. He was commissioned a U.S. Naval Reserve Chaplain on May 10, 1943. He was assigned as a chaplain aboard the U.S.S. Franklin (CV-13), at service in the Pacific Theater of Operations, where he earned the Silver Star after his ship was subjected to a devastating Kamikaze attack in 1945. He was released from active duty in 1945, and was retired from military service as a lieutenant commander in 1951. He was a member of the Methodist Central Texas Conference, continuing in civilian ministry in Texas after the war.