Background: Childcare centres are important environments for promoting physical activity and healthy eating. Blended approaches to professional learning may help overcome existing challenges for educators in promoting these behaviours. This study aimed to test the effect of a blended professional learning program on healthy eating and physical activity in childcare. Methods: Cluster randomized stepped-wedge trial in 15 childcare centres in Tasmania, Australia. Children aged 2-5y who attended at least two days per week were eligible to participate. Random assignment occurred at the centre level. Centre names were drawn out of a hat and then subsequently allocated to one of the three steps. The intervention comprised a 12-week blended professional learning program for educators. The main outcome was centre-level physical activity and healthy eating, assessed using the Environment and Policy Assessment Observation System (EPAO). All data collectors were blinded to step allocation. Analyses were according to intention to treat. The trial was registered with the Australian New Zealand Clinical Trial Registry (ACTRN12618000346279, date registered: 07/03/2018). Results: Centres were recruited between January 2016 and February 2016. All centres were retained for the duration of the study. A total of 313 children were recruited with 291 analysed at the completion of the study (93%). The difference between groups for the EPAO total score was significant at the end of the maintenance period (adjusted difference = 14.63, 95% CI [1.33, 27.92], p = 0.03). Significant differences were found for the percentage of time children spent in light-intensity physical activity at the end of the intervention (adjusted difference = 0.01, 95% CI [0.00,0.01], p = 0.02) and maintenance periods (adjusted difference = 0.01, 95% CI [0.00,0.02], p = 0.04). To the best of the authors knowledge, there were no adverse events. Conclusion: This intervention achieved a sustained improvement in physical activity and healthy eating in childcare centres. Further, it can be easily integrated into existing service provision, especially among centres with limited access to professional learning. Trial registration: The study was registered with the Australian and New Zealand Clinical Trials Registry (ACTRN12618000346279, date registered: 07/03/2018).