Reformed theology affirms the legitimacy of military service through the just war tradition and the doctrine of vocation. The Westminster Confession (Chapter XXIII) addresses the lawfulness of Christians engaging in 'wars that are just and necessary.' The civil magistrate is ordained by God to bear the sword for the protection of the innocent and the punishment of evildoers (Romans 13:4), and Christians may serve as soldiers, judges, or magistrates as a legitimate calling.

Calvin and subsequent Reformed thinkers developed detailed just war criteria and applied them to political analysis. The Belgic Confession (Article 36) teaches that the civil government is established by God to restrain evil and maintain order. Reformed theology is not pacifist and has been historically associated with theories of resistance against tyranny (e.g., the right of lesser magistrates to resist unjust rulers, developed by Reformed thinkers in the Vindiciae contra Tyrannos, 1579). Conscientious objection may be accommodated as a personal conviction but is not the confessional norm.