This article analyses the applicability of two legal principles that originate in municipal legal systems, namely res judicata and lis pendens, in World Trade Organisation (‘WTO’) disputes that involve a conflict of jurisdiction between dispute settlement mechanisms of the WTO and Regional Trade Agreements (‘RTAs’). Ideally, the applicability of non-WTO norms in WTO disputes would be determined on the basis of explicit treaty language, as this would increase the legitimacy of the dispute settlement process. However, since there is no particular WTO provision that explicitly specifies the sources of applicable law in WTO disputes, it is virtually impossible to decisively verify whether WTO law allows the application of non-WTO norms like res judicata and lis pendens in WTO disputes. Thus, whether these norms can be enforced in WTO disputes largely depends on the discretion of WTO tribunals. On this basis, this article first develops a set of criteria against which the applicability of res judicata and lis pendens under WTO tribunals’ inherent powers could be assessed. The article then uses this framework to evaluate whether res judicata and lis pendens can be applied in WTO disputes to resolve jurisdictional conflicts between WTO and RTA dispute settlement.