This paper is intended as a theoretical contribution to Transition Design. By bridging the theoretical foundations of this field with recent contributions from ecosocialism, the paper argues that transition designers need to position themselves within popular movements that aim to satisfy collective needs outside circuits of capital accumulation. While the work is primarily theoretical, it illustrates this strategy through expert interviews by exploring the case of designers working within the Catalonian cooperative movement. As this case shows, by collaborating with popular movements to satisfy their own needs, such as housing, designers are pointing to novel forms of personal and professional engagement with transitions that may transcend the established model of service provision for or within capitalist enterprises.