Purpose: Circular economy advocates innovations that upcycle wastes in the food supply chain to generate high added-value materials. These innovations are not only disruptive and green but also they are often initiated by startups, leading to the emergence of novel open-loop supply chains connecting actors in food and non-food sectors. While earlier research has highlighted the need to seek legitimacy for disruptive innovations to survive and grow, little is known about how these innovations occur and evolve across sectors. This paper aims to elaborate on this mechanism by exploring the function of the circular economy as a boundary object to facilitate legitimacy-seeking strategies. Design/methodology/approach: An exploratory multiple-case research design is adopted and features food waste innovation projects with multi-tier supply chains consisting of a food producer, a startup and a buying firm. The study is investigated from the legitimacy and boundary object lenses. Findings: The findings proposed a framework for the role of a boundary object in enabling legitimacy-seeking strategies for novel food waste innovations. First, the interpretative flexibility of the circular economy affords actors symbolic resources to conduct manipulation strategy to achieve cognitive legitimacy. Second, small-scale work arrangements enable creation strategy for the new supply chain to harness moral legitimacy. Finally, pragmatic legitimacy is granted via diffusion strategy enabled by scalable work arrangements. Originality/value: This paper provides novel insights into the emergence of food waste innovation from a multi-tier supply chain perspective. It also highlights the key role of the boundary object in the legitimacy-seeking process.