To reach the global sustainability goals, multinationals, regardless of origin, play a significant role. Given their market power and globally distributed operations, they have the position to either accelerate or inhibit sustainability changes. Knowledge about how corporate sustainability (CS) develops within internationalization strategies such as post-acquisition integration is, however, sparse. The purpose of this paper was to analyze and evaluate the development of CS strategies of originally distant companies within an international post-acquisition context. The paper drew on the resource-based view (RBV) to provide a holistically integrated framework for the systematic evaluation of CS strategies and applied the framework to a longitudinal in-depth case study. Findings indicated that long-term perspective, partnering approach and, emphases on learning positively influenced the integration process and the maturity level of the common corporate sustainability strategies. In contributing with an in-depth understanding of strategic CS integration within a post-acquisition case, the study generated implications for proactive management in similar post-acquisition contexts. While the focus of this paper was neither on the differences in legislations and regulations as influencing factors nor on the national and organizational culture and their impact on the integration of strategic CS, these are relevant areas of interest, and future research could consider incorporating those into the new evaluation framework.