An Australian national preterm birth prevention programme led to meaningful reductions in preterm and early-term births. Phase 1 was a clinician-led education programme conducted at a population level between 2018 and 2021. Phase 2 added a Breakthrough Series Collaborative involving 59 maternity hospitals across the country between 2022 and 2024. For both phases, outcomes were changes in the rates of preterm (20 weeks + 0 days to 36 weeks + 6 days) and early-term (37 weeks + 0 days to 38 weeks + 6 days), liveborn, singleton births. In Phase 1 (n = 1,479,125 births), the preterm birth rate decreased from 6.40% in 2017 to 5.97% in 2021 (p