Gottfried Wilhelm Leibniz was born in Leipzig (Saxony), on 1 July 1646. His father was Friedrich Leibnüz, his mother Catharina Schmuck. From 1653 until 1661, he attended the Nikolaischule in Leipzig. Between 1661 and 1666, he studied at the university of Leipzig, where he obtained a master's degree in law and completed his habilitation at the Faculty of Philosophy. He earned his licentiate and doctorate in law at the University of Altdorf in 1666. In late 1667, Leibniz became acquainted with Johann Christian von Boineburg, the former Chief Minister to the Elector and Archbishop of Mainz, Johann Philipp von Schönborn. Leibniz served the Elector from 1668 until 1672. After several philosophically productive years in France (1672–1676), he entered the service of Duke Johann Friedrich in Hanover as a court counsellor and librarian. From January 1691, he also held the position of librarian of the Ducal Library in Wolfenbüttel. As a courtier, he devoted considerable time to the ultimately unsuccessful project of establishing mining operations in the Harz Mountains. His lifelong task as a historian was the composition of the Guelf history – the chronicle of the ruling dynasty in Hanover. However, this work remained unfinished due to Leibniz's numerous other pursuits in philosophy and mathematics, as well as his extended stays at the Imperial Court in Vienna in 1889–1890 and 1712–1714. Between 1698 and 1705, Leibniz spent long periods of time in Berlin as a friend and discussion partner of Sophie Charlotte, Electress of Brandenburg. In Vienna, as earlier in Berlin, Leibniz worked towards the establishment of a scholarly society. In August 1714, Duke Georg Ludwig of Hanover departed for London to assume the English throne as Georg I, while Leibniz was required to stay in Hanover and continue work on his overdue Guelf history. His final years were overshadowed by accusations of having plagiarised Newton's calculus. Leibniz died in Hanover on 14 December 1716.

In contrast to the leading natural law theorists of the seventeenth and eighteenth centuries, Leibniz did not articulate his theory of natural law in the form of a book. Consequently, it was only with the exploration of the Leibnizian legacy in the nineteenth century – and particularly with the progress of the Akademie-Ausgabe in the twentieth century – that scholars came to recognise Leibniz as one of the most significant natural law thinkers of the seventeenth century, alongside Hugo Grotius and Samuel Pufendorf (Schneider 1967; Busche 2003). Leibniz first outlined his theory of natural law in an early work, the Nova methodus discendae docendaeque jurisprudentiae (1667). He subsequently developed this theory further in manuscripts later compiled and published under the titles "Elementa juris naturalis" and "Scientia juris naturalis." A more mature formulation of his theory appears in the preface to his diplomatic source edition Codex juris gentium diplomaticus (1693). Thereafter, he applied his theory in numerous writings, including his 1700 treatise "Observationes de principio juris", as well as in his principal theological work, the Essais de théodicée (1710).

The Mainz period (1668–1672) in the early life of Leibniz was decisively shaped by his acquaintance and collaboration with Boineburg. Evidence of their intellectual partnership is found in Leibniz’s handwritten marginalia and notes preserved in Boineburg’s library, in references to Leibniz within Boineburg’s correspondence, and in over eighty mentions of his name and his political, juridical, theological, and philosophical writings in Boineburg’s annotated book entries. This relationship extended beyond the realm of political practice and significantly influenced the development of Leibniz’s scholarly work. His “Christian” theory of natural law was developed in Boineburg's intellectual footsteps, most notably in the manuscripts entitled "Elementa juris naturalis" (1669–1671).

Leibniz developed his theory of natural law in polemical opposition to Pufendorf's secularising doctrine. A guiding thread throughout Leibniz’s critique of Pufendorf is his apprehension regarding political Thrasymachism – that is, the concern that power concentrated in a single authority might become the sole source of law and justice. Within the context of German political thought, Leibniz's responses to Pufendorf’s Severini de Monzambano de Statu Imperii Germanici ad Laelium fratrem liber unus (1667), articulated in Leibniz's Caesarinus Fürstenerius (1677), examine the threat of Thrasymachism through the lens of imperial power structures. This theme resurfaces in his critique of Pufendorf's Jus feciale divinum (1695). Pufendorf's position regarding Reformed predestination in this work is interpreted by Leibniz as an advocacy of a form of divine tyranny in the Epistola ad amicum (1695-96).

Leibniz’s theory of justice, as set out in the preface to the Codex Juris Gentium Diplomaticus (1693), re-emerges in his later critique of Pufendorf’s De officio hominis et civis (1673), specifically in the Monita quaedam ad Samuelis Pufendorfii principia, Gerh. Wolth. Molano directa (1706, published in 1709). The central argument of the Monita is shaped by a polemic against voluntarism – that is, the view that moral obligation originates in the will of a superior. Leibniz’s criticism of Pufendorf in his Essais de Théodicée (1710) prompted various responses from Pufendorf's translator, Jean Barbeyrac, even prior the latter’s celebrated re-edition of the Monita in 1718, accompanied by extensive commentary. This edition marked an often-noted triumph of the Pufendorfian tradition over “Christian” natural law.

Leibniz’s relationship with Pufendorf was not characterised by mere rivalry. Pufendorf did not constitute a competitor whom Leibniz endeavoured to surpass over the course of his career; rather, he served as the essential Other within Leibniz's political thought – an interlocutor through whom Leibniz formulated his own positions in critical dialogue. During Pufendorf’s lifetime, Leibniz’s principal aim was to attract his attention; following Pufendorf’s death, this objective evolved into a concerted effort to counter the increasing influence of Pufendorfian natural law. 

Leibniz’s reception of Pufendorf’s Elementa jurisprudentiae universalis (1660) did not reflect an opposition, but rather a form of complementarity between his own project and that of Pufendorf. Leibniz’s reception and critique of Pufendorf are closely tied to the gradual incorporation of Pufendorf’s works into university curricula. His engagement with De officio hominis and civis (1673), rather than with Pufendorf’s more extensive treatise on natural law, De jure naturae et gentium (1672) arose from the fact that the former had become a standard textbook in academic instruction. 

Leibniz contended that natural law ought to be grounded in transcendent principles. He maintained that every legal question could be resolved through natural law, and that it was possible to ascertain what is just by nature. In the "Elementa juris naturalis", he defended justice as an objective moral standard, in contrast to what he saw as the contingency of justice in Pufendorf’s conception.

In the preface to the "Codex juris gentium diplomaticus" (A IV, 5, 61–5; §§12–15 in Patrick Riley’s English edition), Leibniz, drawing upon Aristotle’s Nicomachean Ethics, Grotius’s De iure belli ac pacis, and his own youthful work Nova methodus, elaborates the three degrees of his natural law theory of justice: “strict right in commutative justice; equity (or, in the narrower sense of the term, charity) in distributive justice; and, finally, piety (or probity) in universal justice”. Rights falling under commutative justice are those for which a legal claim (facultas) may be asserted, whereas those belonging to the second degree pertain to moral claims (aptitudo). The first two degrees of justice govern the conditions of earthly life, while the third – understood as honestas or pietas – is, as Leibniz formulates with reference to Boineburg’s aspirations, the principle that “the law of nature and of the nations should follow the teachings of Christianity (secundum disciplinam Christianorum).” In its political dimension, this theory of justice could, according to Leibniz, serve as the foundation for “a kind of common republic of Christian nations,” under the spiritual leadership of the Pope and the secular authority of the emperor.

The formula “justice is the love of the wise” (justitia est caritas sapientis) encapsulates a central tenet of Leibniz’s conception of justice. Building upon this foundation, Leibniz’s notion of justice assumes a polemical function in two key respects: (1) it resists what he saw as secularizing tendencies to divorce morality from law; and (2) it challenges the voluntaristic grounding of justice found in the works of Hobbes and Pufendorf.

Leibniz’s Monita articulates three principal objections concerning the goal, subject matter, and efficient cause of natural law. With regard to its goal, Leibniz criticises Pufendorf for restricting the validity of natural law to earthly life, thereby disregarding the potential rewards or punishments of moral actions in the afterlife. Concerning its subject matter, Pufendorf confines morally relevant acts to external behaviour alone, whereas Leibniz maintains that internal actions – namely, the sentiments and motivations accompanying deeds – must also be taken into account. The objection concerning the efficient cause constitutes a critique of voluntarism: Pufendorf locates the origin of moral obligation in the will of a “superior” (i.e., God). In response, Leibniz – consistent with his broader metaphysical position – argues that justice is grounded in eternal truths, which are the objects of the divine intellect.