In a world increasingly shaped by climate change and, more broadly, by environmental issues, transport and household mobility play a central role in territorial transition. Given these challenges, local authorities in France and other countries are increasingly implementing fare-free public transport to encouragemodal shift (environmental objective) but also to improvemobility for themost disadvantaged populations (social objective). However, little scientific research has been conducted to assess the true impacts of this policy. This paper analyses the impact of fare-free public transport at weekends introduced in December 2021 by Clermont Auvergne Metropole. Using an econometric model, we compare public transport ridership before and after the policy’s implementation, focusing on the same transport lines, directions, bus stops, time period, and weekend days (Saturday or Sunday). Ridership estimates are based on ticket validation data before the policy and manual counts afterwards. In order to isolate the effect of fare-free public transport, we introduce control variables for key determinants of public transport ridership (e.g., public transport supply, fuel prices, weather data). Given the evaluation period, we also account for potential impacts of the COVID-19 crisis on household mobility. Our results show that fare-free public transport has led to a 47% increase in weekend ridership on the observed routes and stops. We also find that the effect is similar on Saturdays and Sundays, but more pronounced on the tramway line than on the bus lines. To our knowledge, this study is the first econometric analysis of the effect of fare-free public transport in a French city.