Child neglect is the most prevalent form of child maltreatment and represents 79.5% of open child-welfare cases. A recent study found the evidence-based intervention (EBI) SafeCare® (SC) to significantly reduce child neglect recidivism rates. To fully capitalize on the effectiveness of such EBIs, service systems must engage in successful implementation and sustainment; however, little is known regarding what factors influence EBI sustainment. Collaborations among stakeholders are suggested as a means for facilitating EBI implementation and sustainment. This study combines descriptive quantitative survey data with qualitative interview and focus group findings to examine the role of collaboration within the context of public-private partnerships in 11 child welfare systems implementing SC. Participants included administrators of government child welfare systems and community-based organizations, as well as supervisors, coaches, and home visitors of the SC program. Sites were classified as fully-, partially-, and non-sustaining based on implementation fidelity. One-way analysis of variance was used to examine differences in stakeholder reported Effective Collaboration scores across fully-sustaining, partially-sustaining, and non-sustaining sites. Qualitative transcripts were analyzed via open and focused coding to identify the commonality, diversity, and complexity of collaborations involved in implementing and sustaining SC. Fully-sustaining sites reported significantly greater levels of effective collaboration than non-sustaining sites. Key themes described by SC stakeholders included shared vision, building on existing relationships, academic support, problem solving and resource sharing, and maintaining collaborations over time. Both quantitative and qualitative results converge in highlighting the importance of effective collaboration in EBI sustainment in child welfare service systems.