In many mentoring programs, mentor–youth pairs have the latitude to engage in a wide range of activities together across varying community settings. Within this context, program staff are tasked with supporting development of high‐quality relationships between mentors and youth. To date, however, this role of program staff has been largely overlooked in research. The current study investigates potential contributions of program staff to mentoring relationships in the Big Brothers Big Sisters community‐based mentoring program over their first 15 months of relationship development with a sample of 450 mentor–youth pairs that were supported by 76 program staff across 10 agencies. Two‐level analyses (mentoring relationships nested within program staff) examined characteristics and approaches of program staff as prospective predictors of several facets of mentoring relationship quality as reported by youth: closeness, help with coping, youth‐centeredness, growth orientation, and attachment. Staff‐reported work engagement and emphasis on adherence to program guidelines as well as supervisor‐rated staff competence predicted more favorable mentoring relationship quality. By contrast, a nondirective approach to supporting mentors, as reported by staff, predicted lower relationship quality. These findings suggest that further investigation of program staff influences on mentoring relationship development could be fruitful and ultimately provide a basis for enhancing program effectiveness.