International alliance negotiations are now a pervasive feature of the contemporary global economy. As the alliancing firms cross national boundaries to forge cooperative partnerships they face the inevitable necessity of bridging the cultural divide to ensure successful negotiation. Existing research has focused primarily on the impact of national cultural differences in shaping negotiating strategies and ensuing outcomes. Less attention has been paid to how negotiators from different cultures understand and manage the ambiguity of international alliance negotiations. We employ the theoretical lens of sensemaking to understand how negotiators embedded in different cultures manage simultaneously the task and cultural related ambiguity that they are confronted with. This perspective suggests the critical role that ‘tertius iungens’ (the ‘third who joins’) plays in facilitating the negotiation process. The ‘tertius iungens’ represents a form of intermediation that acts as a catalyst in the negotiation process. We propose three alternative types of intermediation, namely, cognitive, affective, and holistic and provide illustrative examples of these types of intermediation. We conclude by highlighting the theoretical and managerial significance of our framework and by suggesting future directions for research.