Low-carbon travel is identified by the low-carbon city pilot (LCCP) policy as an essential method to reduce CO2 emissions. This study is conducted with the primary aim of determining the impact and mechanism of low-carbon city construction on low-carbon travel. In the context of China’s enormous challenges in achieving the “dual carbon” goals, this study takes the implementation of the LCCP policy as a quasi-natural experiment, and uses the progressive difference-in-difference method to empirically examine the effects of low-carbon city construction on bus trips. The results show that low-carbon city construction can significantly promote the increase of bus ridership and the number of bus trips per capita. Both the number of buses and bus ownership ratio are significant mediating mechanisms. Moreover, the effect of low-carbon city construction on bus trips is significant in inland cities and large cities, but not in coastal cities and small and medium-sized cities. The findings verify the effect of LCCP policy on low-carbon travel, and provide important policy implications for further implementing the LCCP policy and accelerating the promotion of low-carbon travel.