We investigate entrepreneurial ecosystems that support circular start-ups and innovation. We argue that entrepreneurial ecosystems for circularity are constellations of existing entrepreneurial and innovation ecosystems that extend across geographies and sectors. Our research question centres on understanding ecosystem intermediation that facilitates the embedding of circular start-ups in different ecosystems and addresses a pertinent gap in the literature about ecosystem intermediation for circular transitions and circular start-ups Focusing on the emerging circular transition in the textiles and apparel industry, we gathered data from in-depth interviews, field observations, and archival documentation over a seven-year period. Our findings show that entrepreneurial ecosystems for circular start-ups are purposefully intermediated at a meta level, combining elements of extant ecosystems to focus on circularity. Drawing on these insights, we conceptualize ecosystem intermediation as connecting diverse ecosystems across geographic and sectoral boundaries. Our study contributes to the literatures on circular entrepreneurship, circular ecosystems, and ecologies of system intermediation as well as provides practical implications for practitioners and policy makers.