In recent decades, quantitative studies on university spinoffs (USOs) have begun to proliferate across disciplines. This study aims to systematically consolidate the measures used in the extant USO research into theoretical constructs, and connect the constructs to the entrepreneurial ecosystem (EE) perspective. In doing so, this study examines the effect of university-level characteristics on the number of USO establishments and USO performance; it also evaluates measurement validities that can reflect constructs. The systematic review and thematic coding reveal four groups of 14 constructs from the measures identified in prior studies: university general characteristics, university research characteristics, university entrepreneurial characteristics, and technology transfer office characteristics. Our meta-analyses indicate that the relationships between the constructs and USO outcomes are generally significant, thereby providing evidence of the convergent and nomological validities of the measures. Research design has a limited impact on the relationships, but country moderates several relationships between university characteristics and USO outcomes. Following our meta-analytic review, we explain the contribution to university entrepreneurship ecosystem research and suggest a theoretically triangulated model for future studies.