He was converted in 1841, after he had already started training for the ministry, and shortly after the death of his father, John Kennedy of Killearnan.
"[5] Alasdair J. Macleod argues that Kennedy "emphasised personal piety, self-examination of religious experience, and theological orthodoxy.
"[7] Kennedy championed exclusive psalmody and the doctrine of limited atonement,[8] and was opposed to confessional revision,[5] union with the United Presbyterian Church (which eventually occurred in 1900), disestablishmentarianism, and instruments in worship.
[4] In 1861, Kennedy wrote The Days of the Fathers in Ross-shire and in 1866 The Apostle of the North, a biography of John Macdonald.
[4] He was also friends with Charles Spurgeon, who after Kennedy's death said of him, "True as steel and firm as a rock, he was also wonderfully tender and sympathetic.