Changes in business strategies are necessary to increase sustainability within business organisations, and change agents are key to bringing about and shaping change. Sustainability change agency involves constant reflection on change agents' roles in complex contexts, a process that arouses emotions for those agents. In this study, we assume a contextual view of change to understand how sustainability change agency develops during change processes and the role of emotions in agency behind strategic changes, such as the implementation of a circular economy. The study is based on interviews with 51 circular economy professionals in Finnish business organisations. By analysing key events and emotions in sustainability change agent (SCA) work, the study contributes to the existing research by showing that initiating and managing sustainability strategies consists of multiple unplanned and unexpected emotional events and experiences. These events and experiences shape SCA's ability and motivation to act for change, leading to continual individual‐level reflection by SCAs, manifesting as ideological, reassuring and fragmenting processes within the larger change process. Such reflection maintains, paralyses, enforces or reshapes their agency, depending on the context.