Public Procurement for Innovation (PPI) is a powerful, underutilized demand-side innovation policy instrument. How this instrument can contribute to meeting societal challenges, which require goal-oriented transformation of socio-technical systems, remains unclear and is explored in this paper. This paper draws on the transitions and PPI literature to propose transformative processes to which PPI can contribute and identifies factors that determine the effectiveness of PPI in meeting societal challenges. The propositions are explored with a case study on the procurement of radically new flood barrier technology, using event history mapping analysis. The paper concludes that, under certain conditions, PPI can contribute to the transformative processes of 1) the articulation of societal demands to direct challenge-driven transformation; 2) the development and production, 3) selection and 4) the diffusion and use of new technologies to meet these societal demands. The paper ends with policy recommendations on how PPI can help meet societal challenges.