ObjectivesPositive effects of mindfulness-based interventions (MBIs) on occupational health have been demonstrated by several systematic review studies during the last two decades. So far, existing reviews excluded mindfulness-informed interventions (MIIs) that build on informal approaches or mixed techniques aiming at improving mindfulness indirectly. To address this research gap, the present comprehensive meta-analysis synthesizes the results of RCTs of MBIs and MIIs conducted in various workplace settings.MethodA systematic literature search was conducted in five electronic databases complemented by manual search. Random-effects models were used to synthesize standardized mean differences (SMDs) for 25 outcomes and seven overarching categories of outcomes, and to detect various temporal effects. Meta-regressions were run to elucidate averageSMDsbetween mindfulness intervention types and intervention and population characteristics, with the goal of detecting sources of heterogeneity and help guide the selection of the most appropriate mindfulness intervention type.ResultsBased on 91 eligible studies (from 92 publications), including 4927 participants and 4448 controls, the synthesis shows that MBIs and MIIs significantly improve mindfulness (SMD= 0.43; 95%-CI[0.33;0.52]), well-being (SMD= 0.63; 95%-CI[0.34;0.93]), mental health (SMD= 0.67; 95%-CI[0.48;0.86]), stress (SMD= 0.72; 95%-CI[0.54;0.90]), resilience (SMD= 1.06; 95%-CI[−0.22;2.34]), physical health (SMD= 0.45; 95%-CI[0.32;0.59]), and work-related factors (SMD= 0.62; 95%-CI[0.14;1.10]). Sensitivity analyses demonstrate a tendency towards smaller effect sizes due to extreme outliers. Effect sizes are stable in short-term follow-up assessments (1-12 weeks) for most outcomes, but not for long-term follow-up assessments (13-52 weeks). Meta-regressions suggest that observable intervention characteristics (e.g., online delivery) and population characteristics (e.g., age of participants), as well as study quality, do not explain the prevalence of heterogeneity in effect sizes.ConclusionsGenerally effective, mindfulness interventions are a useful tool to enhance aspects of employee health. However, because of heterogeneity and risk of bias, studies aiming at high-quality data collection and thorough reporting are necessary to draw firm conclusions.PreregistrationA protocol of this systematic review was registered with PROSPERO (Registration-No. CRD42020159927).Supplementary InformationThe online version contains supplementary material available at 10.1007/s12671-023-02130-7.