Abstract Research infrastructures (RIs) are crucial for scientific progress, innovation, and global development, necessitating international collaboration due to their complexity and cost. Science diplomacy (SD) plays a vital role in facilitating policy design, resource pooling, and governance for effective collaboration in RIs. Multinational cooperation in RIs provides financial relief and access to advanced technology and promotes cutting-edge research, benefiting scientific development and socioeconomic growth. This article explores the role of SD in European-Latin American and Caribbean (EU-LAC) RI collaboration, underscoring the importance of diverse and equitable inter-RI collaboration. The study addresses challenges in EU-LAC collaboration, emphasizing the unequal development of RIs and the need for political support. Through interpretive policy studies and stakeholder interviews, the research contributes to formulating an ideal type and a feasible scenario for sustainable collaboration, discussing policy implications and highlighting the pivotal role of SD in successful international RI partnerships.