Miley had graduated from Augusta College and, as a Methodist pastor, had held nineteen different pastoral appointments. He served as chair of systematic theology at Drew University in Madison, NJ beginning in 1873, after his brother-in-law, Randolph Sinks Foster, left the seat to become a Bishop.
Miley was one of "the Great Five" revered professors who led Drew for decades, along with Henry Anson Buttz, George Crooks, James Strong, and Samuel Upham. He viewed the theology of John Wesley as foundationally excellent but in need of an update for the modern world, and endeavored to do so.
He was the author of Systematic Theology (1892, ISBN 0943575095), a two-volume work which served as a key text for Methodist seminarians for decades. He also authored The Atonement in Christ (1879), in which he demonstrated what he believed were severe Biblical and theological problems with commonly held theories on the doctrine of the atonement such as the punishment or penal substitution view of Calvinism and the moral example view of Pierre Ablard, developing a strong moral government theology which was thoroughly Wesleyan and Arminian, heavily reliant on the work of Hugo Grotius. The book remains one of the most important works regarding atonement theology.