Parental engagement in parenting programs is essential for good outcomes but can be challenging for many families. In low- and middle-income countries, where resources are limited and there are fewer support services, there is little research examining the factors that influence engagement. This mixed-methods study explored factors associated with parent engagement, as well as barriers and supports, in a pilot evaluation of a parenting program with 140 parents in North Macedonia, Republic of Moldova, and Romania. The relationship between various quantitative types of engagement (e.g., premature drop-out, participation) and a range of demographic, personal, and implementation factors were examined. Qualitative parent interviews explored barriers and supports to program engagement. Implementation variables (e.g., phone calls with parents, program fidelity and text messages sent to parents) were consistently positively associated with different types of engagement after controlling for other factors. Parents of boys, being a victim of intimate partner violence, more children in the household and better parental well-being were positively associated with premature drop-out whilst having a child enrolled in school was positively associated with participation. Barriers included logistical factors such as timing and lack of childcare facilities. Factors that increased engagement included facilitator skills/support, weekly text messages and phone calls and engagement strategies such as transport and childcare. The results emphasise the importance of implementation factors in increasing parent engagement in parenting programs and will help to inform the next phase of the project as well as other family-support initiatives in the three countries. The trial is registered on ClinicalTrials.gov (ID: NCT03552250).