Private sector actors both enable and inhibit sustainability-oriented policies at multiple scales. Yet, research on business sustainability predominantly emphasizes large corporations, while contributions of small- and medium-sized enterprises (SMEs) are downplayed. Consequently, there is a dearth of conceptual tools to explain how SMEs construct and advance collective sustainability goals. The aim of this paper is to identify how SMEs participate in urban sustainability politics. To do so, we analyse empirical data collected through interviews with 76 businesses operating in Toronto, Vancouver, and London. Our results demonstrate that SMEs shape sustainability dynamics by participating in formal political processes and social movements, and by constructing and contesting discourses. Contrary to past research, our study highlights the ability of these firms to navigate urban decision-making processes and align business operations with political beliefs and identities. In light of these findings, we point to the need to recognise SMEs as actors with political agency.