Abstract Background To investigate the effect of an early childhood obesity prevention intervention, incorporating a parent modelling component, on fathers’ obesity risk-related behaviours. Methods Cluster randomized-controlled trial in the setting of pre-existing first-time parents groups organised by Maternal and Child Health Nurses in Victoria, Australia. Participants were 460 first-time fathers mean age = 34.2 (s.d.4.90) years. Dietary pattern scores of fathers were derived using principal component analysis, total physical activity and total television viewing time were assessed at baseline (infant aged three to four months) and after 15 months. Results No significant beneficial intervention effect was observed on fathers’ dietary pattern scores, total physical activity or total television viewing time. Conclusion Despite a strong focus on parent modelling (targeting parents own diet, physical activity and television viewing behaviours), and beneficial impact on mothers’ obesity risk behaviours, this intervention, with mothers as the point of contact, had no effect on fathers’ obesity risk-related behaviours. Based on the established links between children’s obesity risk-related behaviors and that of their fathers, a need exists for research testing the effectiveness of interventions with a stronger engagement of fathers.