The effects of job stress and burnout pose a large threat to employee health and organisational success in modern society. Company spending is highly affected by increased employee turnover, absenteeism, stress-related sick leave, and other issues that arise from exposure to workplace stress. For these reasons, organisations often implement stress management initiatives such as mindfulness-based interventions (MBIs) to help manage stress and prevent burnout. Mindfulness-based interventions have already provided researchers with significant results in workplace stress reduction, therefore, the purpose of this present study was to examine this relationship whilst investigating exercise as a potential moderating variable. This was achieved by conducting a meta-analysis of 17 controlled and uncontrolled studies and calculating a combined effect size using meta-analysis software. The combined effect size (Hedge’s g) for all controlled mindfulness-based intervention studies was 1.366 (95% confidence interval = 0.678, 2.055), a very large, significant effect. The combined effect size for controlled studies whilst accounting for exercise as a moderator was 0.992 (95% confidence interval = 0.386, 1.597), which also indicates a very large effect. Due to a lack of studies in the extant literature which incorporated moderate to high intensity exercise, it was not possible to examine the impact of different intensities of exercise on workplace mindfulness-based interventions. In order to gain a more comprehensive understanding of the effects of mindfulness, future research needs to incorporate exercise of moderate to high intensities, as well as examine the potential mediators of the main relationship between mindfulness, job stress, and burnout. This meta-analysis should encourage organisations to use mindfulness-based interventions to improve employee well-being.