Public procurement of innovation (PPI) is increasingly recognised as a powerful demand-side instrument for generating solutions to complex societal challenges. Yet realising this transformative potential requires innovations to scale beyond isolated implementation contexts. We contribute to the literature by bridging innovation scaling and market shaping perspectives to develop a novel conceptual framework for scaling in the context of PPI. We identify three distinct scaling modes: ‘market acceleration’, where buyers stimulate business growth by facilitating innovation development, adoption, and dissemination across contexts, ‘market building’, where buyers aggregate public sector needs and broaden the scope of PPI, and ‘market transformation’, where buyers embed innovations by reshaping socio-technical systems. Through empirical investigation of twelve publicly-funded PPI projects in Finland, we identify scaling practices used by public buyers throughout the procurement lifecycle, spanning information dissemination, demand coordination, and institutional norm-shaping. Our findings advance theoretical understanding of how public procurement shapes innovation scaling, while providing practical insights into mechanisms through which public buyers can strategically influence market development.