Background <p>Burnout in midwifery is widespread globally, influencing workforce attrition and undermining maternity service provision. Large-scale systematic and structural reforms are necessary but time-consuming. Meanwhile, midwives need immediate support for wellbeing to enable them to make sense of their workplace, workload and their practice. This research aimed to examine the impact of Group Clinical Supervision (GCS) on burnout among midwives.</p> Methods <p>This superiority cluster randomised controlled trial studied registered midwives working at public maternity services in metropolitan New South Wales, Australia. Managers, agency staff and midwifery students were excluded. Sites were randomised electronically; midwives at intervention sites received monthly, hour-long, face-to-face GCS sessions. All participating midwives were surveyed six-monthly between June 2022 and November 2024. The primary outcome was burnout, measured with the Copenhagen Burnout Inventory, including sub-dimensions – personal, work-related and client-related burnout – and analysed using a mixed-effects linear regression model adjusted for covariates. Secondary outcomes were perceptions of workplace culture and the GCS sessions. Only the statistician analysing data was blinded to group allocation.</p> Results <p>Twelve maternity services were enrolled, with 980 intervention participants and 1009 controls. Burnout rates were similar for both arms, but following adjustment for covariates, the intervention was associated with a small but statistically significant reduction in overall burnout scores: mean 47.3 for midwives at intervention sites (<i>n</i> = 882) and 50.0 for controls (<i>n</i> = 913), β=-2.7, 95% CI: -4.7 to -0.6] (<i>p</i> = 0.013). Specifically, work-related burnout was 3.0% points lower in the intervention group (<i>p</i> = 0.022), although reductions in client-related and personal burnout were not statistically significant. Most participants perceived their workplace culture positively, although the control group rated their overall workplace culture significantly more highly (<i>p</i> &lt; 0.001). No unintended or harmful events occurred.</p> Conclusion <p>This study showed that regular GCS can lower overall and work-related burnout in midwives. The overall rate of 51.5% was similar to or lower than other studies, with similarly lower rates among older midwives. There is an urgent need for systemic changes in maternity services, encompassing institutional support strategies to mitigate burnout so that staff can better manage their professional demands.</p> Trial registration <p>10/05/2021 with Australian New Zealand Clinical Trials Registry - ACTRN12621000545864p.</p>