The issue of the relationship between Calvinism and assurance is one that has vexed historians and theologians alike. David W. Miller, a distinguished historian of religion, once argued that Calvinism and assurance of personal salvation were wholly incompatible. This article seeks to use a biographical case study of one of Ulster Presbyterianism's most significant figures in order to illuminate our understanding of a much wider historiographical debate. The 1859 Revival was supposed to have furthered the cause of evangelicalism, while Isaac Nelson's denomination (the Presbyterian Church in Ireland) was its main beneficiary. Nelson, however, did not believe that the Revival was congenial to the orthodoxy of evangelical Presbyterianism. In particular, he took exception to views of assurance popularized during this movement, which appeared to be more in line with Methodist Arminianism than with Reformed orthodoxy. In the years subsequent to the Revival, debate raged within the Irish Presbyterian Church as to whether or not revivalist notions of assurance were compatible with the Westminster Confession. The anti‐revivalist William Dobbin charged the revivalist Robert Crawford with holding heterodox opinions, only for the latter to be acquitted by the General Assembly. Most existing scholarship on the Assurance Controversy has concentrated on the debate between Dobbin and Crawford; this tendency has unhelpfully obscured both important nuances and the wider significance of the debate. By concentrating on the arguments of Nelson, the broader issue of confessional Calvinism's fraught relationship with popular evangelical conceptions of Christian assurance can be understood more clearly.