Small and medium-sized enterprises (SMEs) often face significant barriers during internationalisation. This paper aims to examine how formal industry clusters, defined as groups of similar firms in a specific geographic area, can reduce these barriers and enable successful global expansion for SMEs. It highlights the role of legitimacy within these clusters, a crucial aspect that can directly influence SMEs' ability to attract global partners and investors. The paper focuses on the life sciences industry within the developed contexts of Scotland and Denmark, through a qualitative approach involving interviews with 17 CEOs and founders of SMEs in this industry. The findings offer valuable insights by extending legitimacy theory, highlighting how industry clusters facilitate SMEs' legitimacy, and addressing challenges like resource accessibility, adaptations, and partnerships. It emphasises the dynamic relationship between internationalisation and legitimacy, noting its variability across different internationalisation stages.