John Wesley (1703-1791) was a theologian and practitioner of mission. The theological sophistication of his missiology has never been fully appreciated for three reasons: 1) Wesley seldom used the language of “mission,” 2) he intentionally masked the depth of his learning in the interest of “plain, sound English,” and 3) interpreters assumed that as an evangelist, Wesley could not be taken seriously as theologian. Quite to the contrary, this article shows the depth and sophistication of Wesley’s doctrinal and missiological thinking. Reviewing Western Christian theology from the first century to our day, this article examines the close use of Irenaeus by Wesley, which carries high potency for Christian fidelity, discipleship, theological integrity, authentic mission, and Spirit-powered transformation in persons and culture.