Background: Identifying factors that may contribute to the use of programs following the completion of training by practitioners is of practical and theoretical importance. Aim: This study examined the role of social identity and self-efficacy in contributing to the delivery of an evidence-based parenting program. Methods and Procedures: A sample of 63 multi-disciplinary professionals trained in the Stepping Stones Triple P-Positive Parenting Program, for parents of children with developmental disability, as part of a statewide roll-out were interviewed two years after training. Data on the number of hours of delivery during the 2-year period was analysed along with quantitative data obtained during interviews that assessed professionals’ self-efficacy and social identity as a Stepping Stones professional. Outcomes and Results: Social identity was associated with the use of SSTP in an independent analysis, but the association was no longer significant when other factors were included in a regression model. Self-efficacy predicted the use of SSTP and was found to be a mediator in the relationship between social identity and use of SSTP. Conclusions and Implications: This first investigation into the role of social identity in the implementation of evidence-based parenting programs showed that social identity could play an important role. The role of self-efficacy in predicting program use was further supported in this study and the mediator function of self-efficacy is explored. The practical and theoretical implications of the role of self-efficacy and social identity in the training of professionals are discussed.