Abstract Background Despite evidence supporting the safety of vaginal birth after caesarean section (VBAC), rates are low in many countries. Methods OptiBIRTH investigated the effects of a woman-centred intervention designed to increase VBAC rates through an unblinded cluster randomised trial in 15 maternity units with VBAC rates < 35% in Germany, Ireland and Italy. Sites were matched in pairs or triplets based on annual birth numbers and VBAC rate, and randomised, 1:1 or 2:1, intervention versus control, following trial registration. The intervention involved evidence-based education of clinicians and women with one previous caesarean section (CS), appointment of opinion leaders, audit/peer review, and joint discussions by women and clinicians. Control sites provided usual care. Primary outcome was annual hospital-level VBAC rates before the trial (2012) versus final year of the trial (2016). Between April 2014 and October 2015, 2002 women were recruited (intervention 1195, control 807), with mode-of-birth data available for 1940 women. Results The OptiBIRTH intervention was feasible and safe across hospital settings in three countries. There was no statistically significant difference in the change in the proportion of women having a VBAC between intervention sites (25.6% in 2012 to 25.1% in 2016) and control sites (18.3 to 22.3%) (odds ratio adjusted for differences between intervention and control groups (2012) and for homogeneity in VBAC rates at sites in the countries: 0.87, 95% CI: 0.67, 1.14, p = 0.32 based on 5674 women (2012) and 5284 (2016) with outcome data. Among recruited women with birth data, 4/1147 perinatal deaths > 24 weeks gestation occurred in the intervention group (0.34%) and 4/782 in the control group (0.51%), and two uterine ruptures (one per group), a rate of 1:1000. Conclusions Changing clinical practice takes time. As elective repeat CS is the most common reason for CS in multiparous women, interventions that are feasible and safe and that have been shown to lead to decreasing repeat CS, should be promoted. Continued research to refine the best way of promoting VBAC is essential. This may best be done using an implementation science approach that can modify evidence-based interventions in response to changing clinical circumstances. Trial registration The OptiBIRTH trial was registered on 3/4/2013. Trial registration number ISRCTN10612254.