A substantial literature explains the adoption of climate change acts and their impact on climate policy once adopted. In contrast, we know very little about the processes leading to the non-adoption of climate change acts and the subsequent consequences for climate policymaking. This contribution aims at filling this gap by analysing the non-adoption of the Belgian bill for a climate change law. Proposed in February 2019, the Belgian bill for a climate change law was debated but then rejected very soon after, at the end of March 2019. Taking the non-adoption of the Belgian bill on climate change as an enlightening case study, this contribution investigates the impact of climate change act non-adoption on climate policies by: (i) questioning how climate change acts are drafted, and the role of academic experts for such a task in a context of climate emergency; (ii) analysing the reception and discussion of the bill on climate action, including within civil society; and (iii) tracing the follow-up actions undertaken in the wake of the bill’s non-adoption. The research relies on documentary analysis (climate change act drafts and final text, parliamentary discussions, non-governmental organizations’ archives), interviews with key actors and an exploratory questionnaire with climate activists. Although it was not adopted, we argue that the climate change act project has opened new opportunities to rethink expertise and climate mobilization in Belgium. Key Policy Insights Even when climate change bills fail, they can still have important political or policy effects in the future by raising awareness for the impacts of climate change. When proposing new laws, academic experts should be well informed about the timing and conditions of the political agenda. Consultations with civil society on climate change law projects would increase public awareness and pressure for adoption. Including other important societal causes related to social, economic, decolonial and gender issues, would be key to broadening the impact of ...