Abstract The Regional Comprehensive Economic Partnership (RCEP) is one of the most important mega-regional trade agreements signed to date. Yet, it failed to include an Investor-State Dispute Settlement (ISDS) mechanism in its investment chapter. What explains this omission? To unpack this, we examine international negotiations as a two-step process. In the first stage, we theorize that initial preferences towards ISDS are based on countries’ orientation toward foreign direct investment (FDI), experience with ISDS, and past treaty practice. Second, we theorize that during protracted negotiations, adverse regime developments and domestic politics can have a profound impact on treaty design. To test our framework, we examine the RCEP negotiations. Our analysis shows that mounting cases as well as the eroding norm of ISDS in other treaties lowered support for ISDS as the negotiations progressed. Then, a change of government in Malaysia shifted that country’s position dramatically, which tipped the balance against ISDS in the final round of negotiations. Our findings have important implications for the international investment regime. They highlight the factors that determine countries’ initial preferences while also demonstrating the importance of developments during the negotiations, which can lead to the abandonment of the institutional status quo.