This study examines how internal CEO alliances, defined as social and structural ties between CEOs, subordinate executives, and board members, influence corporate carbon performance. Drawing on data from 36 countries over the period 2002–2023, we find that strong internal alliances are associated with weaker carbon performance, suggesting that concentrated internal power may hinder firms’ emission reduction efforts. However, this adverse effect is significantly moderated by various organizational and institutional factors. Specifically, it is attenuated in contexts characterized by stringent environmental regulation, robust media oversight, high regulatory quality, and greater board gender diversity. At the individual level, CEO characteristics such as hometown affiliation and older age also appear to reduce the negative influence of internal alliances. These findings advance our understanding of how CEO power dynamics interact with external and internal governance mechanisms to influence firms’ climate-related outcomes.