Beyond Formal Consent: Systemic Integration and the Interpretation of Treaty-Based Due Diligence Obligations

Treaty-based due diligence obligations, as obligations of conduct requiring a State’s best efforts, are pivotal in addressing globalized risks. This Article argues that systemic integration under Article 31(3)(c) of the Vienna Convention on the Law of Treaties is imperative to prevent these obligations from being reduced to hollow concepts or procedural formalities. However, judicial reliance on inapplicable treaties and non-binding instruments has created a tension between the coherence of the international legal system and the principle of State consent. In an attempt to justify such practice, this Article proposes a refined understanding of the State consent requirement by shifting the focus from the formal binding force of external instruments to their evidentiary value in concretizing treaty-based due diligence obligations. By analyzing recent international jurisprudence, this Article demonstrates that external references function as epistemic benchmarks for objective capacity, as bases for normative presumptions under the principle of good faith, and as evidentiary markers of feasibility through peer-based comparability. This Article concludes that such an interpretative approach does not undermine State consent but rather operationalizes the State’s initial consent to treaty-based due diligence obligations. It turns out that interpreting due diligence obligations through systemic integration is at once desirable in principle, effective in application, and legitimately grounded. Ultimately, this interpretative approach offers a robust framework for operationalizing due diligence obligations and fostering the co-evolution of international rules and standards.