The thesis establishes that the political liberty proposed by the Levellers during the English Civil Wars of the 1640s was derived from a theological doctrine of Christian liberty, rooted in Christology and Ecclesiology, and informed by various legal and philosophical traditions. The work is structured around an examination of the sources of Leveller political thought and a discussion of some implications of this for modern understandings of political liberalism. The thesis argues that a major key to understanding the Levellers is to see the way in which they utilised existing streams of thought, whilst both synthesising and modifying these. These diverse intellectual currents include the English common law, free grace theology, early General Baptist ecclesiology, and natural law and canon law traditions. The Levellers combine these to give rise to the idea that the state should be strictly limited by the individual’s freedom, rights, and contractual consent. The thesis takes great care with the religious sources, in order to avoid a number of current misreadings, especially with respect to theological ideas, ecclesial groupings, and terminology, particularly in relation to Puritanism. The opposition to fundamental elements of Puritanism will be shown to be a hermeneutic key that unlocks our understanding of the Levellers. The research calls into question particular socialist readings of the Levellers. It also implicitly shows that the rejection of liberalism by certain modern Christian thinkers is based on an unnuanced view of political liberalism. Equally, the work provides a corrective to some recent secular accounts of political liberalism that see the historical roots of liberalism in a reaction to the church and religion.