Conservation scientists are increasingly recognizing the need to evaluate the effectiveness of interventions to improve human–wildlife coexistence across different contexts. Here we assessed the long-term efficacy of the Long Shields Community Guardians programme in Zimbabwe. This community-based programme seeks to protect livestock and prevent depredation by lions Panthera leo through non-lethal means, with the ultimate aim of promoting human–lion coexistence. Using a quasi-experimental approach, we measured temporal trends in livestock depredation by lions and the prevalence of retaliatory killing of lions by farmers and wildlife managers. Farmers that were part of the Long Shields programme experienced a significant reduction in livestock loss to lions, and the annual number of lions subject to retaliatory killing by farmers dropped by 41% since the start of the programme in 2013, compared to 2008–2012, before the programme was initiated. Our findings demonstrate the Long Shields programme can be a potential model for limiting livestock depredation by lions. More broadly, our study demonstrates the effectiveness of community-based interventions to engage community members, improve livestock protection and ameliorate levels of retaliatory killing, thereby reducing human–lion conflict.