The transition to a Circular Economy (CE) promises improved work quality, social inclusion, and solutions to climate breakdown, resource scarcity, and biodiversity loss. However, its social sustainability implications particularly on a global scale remains unclear. Given the important role of Multi-National Corporations (MNCs) in this transition, it is crucial to examine their integration of social sustainability in relation to their transition to CE. This paper enhances understanding of MNCs' engagement in fostering a just transition to CE. Semi-structured interviews (n=22) were conducted with an MNC and actors within its innovation ecosystem in both a high-income and a lower middle-income country (LMIC). The study reveals (1) the early, substantial, yet fragmented efforts by the MNC to integrate social sustainability and CE, distinguishing between compliance and strategic practices; (2) the untapped potential in subsidiaries and suppliers in LMICs; (3) contrasting perceptions concerning the implications and handling of procedural and distributional justice of CE, currently undiscussed. The study advances the emerging discourse on CE and justice and the role of social sustainability practices in providing opportunities and challenges for a just and inclusive CE innovation ecosystem.