This paper investigates how innovation intermediaries promote institutional change to facilitate public procurement of innovation (PPI). Several of the PPI implementation challenges reported in prior research originate in the institutional architecture underpinning demand articulation, and innovation procurement and adoption processes. We conceptualise innovation intermediaries as institutional entrepreneurs who seek to create new institutions or adjust existing ones to support PPI implementation. We report the results of two case studies of intermediaries facilitating PPI in the UK defence and health sectors, respectively. We contribute to PPI intermediation literature by showing that intermediaries address prevalent institutional failures through four types of institutional entrepreneurship activities: boundary spanning; advocacy; design of change; and capacity building. We elucidate, in particular, the role of individuals within intermediaries, as agents who learn about failures and adapt their institutional work over time. In doing so, these managers go beyond the remit and goals of the organisations they represent. The findings add to our understanding of how intermediaries support demand articulation for PPI by showing that their institutional work is also aimed at designing generic methods and processes to improve what is asked for, and how. We furthermore reveal conditions influencing the effectiveness of intermediaries’ efforts to realise institutional change, thereby extending research on institutional entrepreneurship in PPI settings.