Paul was the son of Paul and Harriet (Wannamaker) Hardin. He attended Wofford College in 1920, where he studied law and then to Candler School of Theology, Emory University in 1924, where he received his divinity degree in 1927. Hardin was ordained Deacon in 1929 and Elder in 1931. He was assigned to pastorates in North Carolina and in 1949 he was appointed to Birmingham, Alabama First Methodist Church. Hardin was elected bishop on July 15, 1960, at the Southeastern Jurisdictional conference. For many years he was the resident bishop of the Columbia (South Carolina) area. From 1961 to 1964 he also had charge of the Alabama-West Florida Conference following the death of Bishop Bachman Gladstone Hodge.