Research summary: Cross‐border acquisitions may raise legitimacy concerns by host‐country stakeholders, affecting the acquisition outcomes of foreign firms. We propose that theorization by local regulatory agencies is a key mechanism that links legitimacy concerns with acquisition outcomes. Given that theorization is time consuming and its outcome is uncertain, we argue that state‐owned foreign firms experience a lower likelihood of acquisition completion and a longer duration for completing a deal than other foreign firms. Moreover, we introduce a set of firm characteristics (target public status, target R&D alliances, and acquirer acquisition and alliance experiences) that may affect the threshold level of legitimacy, thereby altering the proposed relationships. Our framework and findings provide useful implications for institutional theory on its core concept of legitimacy. Managerial summary: Cross‐border acquisitions by state‐owned foreign firms may lead to national security concerns and thus debates and discussions among local regulatory agencies. We argue that such institutional processes may reduce the likelihood of acquisition completion and prolong the duration of acquisition completion. Using cross‐border acquisitions in the United States, we find that acquisitions by state‐owned foreign firms are not less likely to be completed than acquisitions by other foreign firms, but they take more time to be completed. Moreover, state‐owned foreign firms are less likely to complete an acquisition when the target firm has more R&D alliances. However, their acquisition experience and alliance experience in the host country increase the likelihood of acquisition completion, whereas their alliance experience alone shortens the acquisition duration. Copyright © 2016 John Wiley & Sons, Ltd.