Using a relational view of international business, we explore how migrant inventors influence cross-border mergers and acquisitions (M&As) by research and development (R&D) firms. We hypothesize that the international social networks of migrant inventors help their employers find and integrate relevant knowledge from acquisition targets in the inventors’ home countries. We test this hypothesis with several conditional logistic regressions on a large sample of deals and control cases. Our findings indicate that the impact of migrant inventors is stronger when the countries involved are far apart, when targets are in countries with weak administrative or legal systems, and when targets are innovative, belong to high-tech sectors, or are in the same sector as the acquirer. This impact is also greater for full acquisitions compared to partial ones.