This thesis examines the life and work of Thomas Gillespie and the origins of the Relief Church in eighteenth century Scotland, within the wider context of the evangelical movement both within and without the Church of Scotland. We begin in the first chapter by investigating the early influences on Gillespie's life, and seek to analyse Gillespie's intellectual and spiritual development within the wider context of Scottish religion. We also look at the profound impact of his brief, but significant, period of study at Philip Doddridge's theological Academy in Northampton. Finally, we consider the beginning of his pastoral ministry in Carnock. In the second chapter we focus on the Combuslang Revival in 1742, including the significant factors which contributed to the event, the impact it made upon Evangelicals within the Church of Scotland, and the divisions it created between Evangelicals in the Church of Scotland and the Secession Church. The third chapter examines the events surrounding Gillespie's deposition from the ministry of the Church of Scotland in 1752. This includes a discussion of the different approaches which members of the Moderate and Popular parties took towards the issue of patronage, especially as illustrated by the controversy surrounding the Inverkeithing settlement. Chapter four looks at the two further disputed pastoral settlements, in Jedburgh and Colinsburg, which led directly to the formation of the Presbytery of Relief. In chapter five we examine Gillespie's preaching and pastoral ministry, and consider the major emphases of his ministry and the themes which were vitally important to him. Chapter six develops an interpretation of Gillespie's theology in its relationship to the Reformed Theology of the Westminster Confession of Faith and the ethos of the Enlightenment. Finally, chapter seven examines the consolidation of the Relief Church. In examining the state of the Relief Church at the time of Gillespie's death, we will also consider the reasons why he had become disillusioned with the movement which had grown to the point when it was outwith his control and influence, and also why many members of the Relief Church may have become disillusioned with him.