Poor participant engagement undermines individual and public health benefits of early intervention programs. This study assessed the extent to which three types of engagement (participant enrolment, retention and involvement) were influenced by individual, program and contextual factors. Data were from a cluster randomised controlled trial (N = 1447) of a community-based parenting program, delivered at two levels of intensity (group sessions with and without individualised home coaching) conducted in Victoria, Australia. Individual (parent and family) factors and program factors were assessed by parent report and administrative records, and contextual factors by area-level population statistics. Data were analysed using multilevel logistic or linear regression models. Individual and contextual factors predicted enrolment, while family and program factors were more influential on program retention and parents' active involvement. Provision of individualised support was important to all forms of engagement, particularly for families experiencing the greatest barriers to participation. These findings indicate that different strategies are required to effectively support families in the processes of enrolling, continuing to attend and actively participating in early intervention programs.