John Leadley Dagg (1794–1884), born in Loudoun County, Virginia was an American Baptist theologian.

He was ordained as a minister in November 1817 and eventually served as the pastor of the Fifth Baptist Church in Philadelphia for nine years.

Dagg left Tuscaloosa in January 1844 to become president of Mercer University.

[2] His additional books included Treatise on Church Order (1858), Elements of Moral Science (1859), and Evidences of Christianity (1869).

[3] Dagg moved to Alabama to live near his daughter, where he died in Hayneville in 1884.