Abstract
International arbitration now stands at the center of transnational commercial governance, and within this framework, lex mercatoria has re-emerged as one of its most contested normative foundations. Often described as a body of transnational customs, usages, and general principles operating beyond any single sovereign system, it is credited with supplying commercially rational standards, interpretive coherence, and essential gap-filling functions in cross-border transactions. Yet its claim to autonomy remains doctrinally unsettled. This article re-examines the historical trajectory, conceptual boundaries, and sources of lex mercatoria, tracing its medieval origins, twentieth-century revival, and contemporary entanglement with institutional arbitration and sophisticated soft-law frameworks, including the extension of the International Institute for the Unification of Private Law (UNIDROIT) Principles into emerging domains such as blockchain, smart contracts, and digital assets (Jovanović, 2025). It argues that although lex mercatoria displays genuine normative vitality—manifest in merchant practice, arbitral reasoning, and harmonizing instruments—its autonomy is structurally constrained. Rather than constituting an independent legal order, it operates as a semi-autonomous transnational normative regime that shapes expectations and supplements domestic law while remaining dependent on state enforcement, public policy oversight, and institutional legitimacy. Rejecting both celebratory claims of independence and dismissive critiques of irrelevance, the analysis reconceptualizes lex mercatoria as a pragmatic juridical formation co-produced by commercial actors, arbitral institutions, and sovereign legal systems.