Background and Objective: School-based health-promoting interventions (HPIs) aim to support youth development, but few interventions are formally evaluated and schools may often rely on subjective indicators to decide whether or not to maintain an intervention long-term. Identifying factors that contribute to or hinder the perceived success of HPIs could facilitate their adaptation, improve implementation. The objective of this study was to identify factors in three domains (school characteristics, characteristics of the HPI, and factors related to planning and implementation) associated with perceived success of HPIs as reported by school principals in elementary schools. Methods: Data were drawn from PromeSS, a cross-sectional study of school principals in a convenience sample of 171 public elementary schools across Quebec, Canada. School board and school recruitment spanned three academic school years (2016-2019). Data on school and participant characteristics, HPI characteristics, variables related to HPI planning and implementation and perceived success of the HPI were collected in two-part, structured telephone interviews. Descriptive statistics were used to characterize schools and study participants. Twenty-eight potential correlates of perceived HPI success were investigated separately in multivariable linear regression modelling. Results: Participants generally perceived HPIs as highly successful. After controlling for number of students, language of instruction, school neighbourhood and school deprivation, we identified five correlates of perceived success: lower teacher turnover; higher scores for school physical environment; school/teacher commitment to student health; principal leadership; and school having developed the HPI de novo (vs. adopting it from an external source). Conclusions: Because school principals are key players in the school environment and instrumental in HPI implementation and sustainability, we contend that their perception of HPI effectiveness is a key indicator of the potential usefulness of HPIs. If replicated, these factors should be considered by HPI developers and school personnel when planning and implementing HPIs in elementary schools.