Objectives While interventions using mindfulness have been effective in treating burnout, the mechanisms of change need more research. This study investigated which of five mindfulness facets (observing, describing, acting with awareness, non-judging, and non-reacting) mediated the intervention effects on three burnout dimensions (exhaustion, cynicism, and reduced professional efficacy) during an 8-week mindfulness-, acceptance-, and value-based (MAV) intervention and a 10-month follow-up. Methods The participants were a heterogeneous sample of employees suffering from burnout (n = 202, 80% women, mean age = 47.5 years). Latent change score modeling was conducted for each combination of the mindfulness facets and the burnout dimensions. Confidence intervals were calculated for the coefficients in the models. Results The modeling results showed that mindfulness improvement during the intervention mediated burnout alleviation during both the intervention and the 10-month follow-up. A large spread of mindfulness facets mediated changes in all the burnout dimensions during the intervention (all for cynicism, all except describing for exhaustion, and all except observing for reduced professional efficacy). The improvement in non-judging skills mediated the reductions in all burnout dimensions during the follow-up. For exhaustion, it was the only significant mediator during the follow-up, whereas for cynicism and reduced professional efficacy, describing and observing were additional mediators. Conclusions Improving mindfulness facets using a MAV intervention had significant long-term effects on burnout in this study. Non-judging is possibly the most important mindfulness facet to improve in burnout interventions, given that it mediated the changes in all burnout dimensions during both the intervention and 10-month follow-up.