Purpose: This paper aims to examine how innovation intermediary activities increase relational proximity between start-ups and foreign partners to support start-up internationalization. Design/methodology/approach: The paper applies a case study methodology to examine an international network of innovation intermediaries in the resources sector. Interviews were conducted with 59 start-ups, corporate and intermediary managers in four countries, supplemented by secondary data. A two-stage analysis process was performed to first identify activities relating to start-up internationalization and then apply a theoretically derived coding framework based on five proximity dimensions. Findings: The case identifies several innovation intermediary activities, which facilitate relationship development between start-ups and partners in new markets. Findings outline how activities increase relational proximity across different dimensions, while also indicating a number of interrelations between dimensions, given the complexity of international business relationships. Originality/value: This paper establishes interdisciplinary bridges between business networks, international business and economic geography perspectives. It provides a valuable empirical foundation for relational proximity, demonstrating its application to understanding start-up internationalization and its influence by intermediary-led activities.