This mixed-methods community-based participatory research generated knowledge of school staff perceptions of the facilitators of and barriers to implementation of a Canadian First Nation school’s healthy nutrition policy. Themes derived from seven qualitative staff interviews were integrated with quantitative data derived from 28 staff surveys. The Medicine Wheel was used to describe results, as it provided a non-hierarchical and relational way to categorize all components and stakeholders of nutrition policy implementation. Factors that facilitated policy implementation were associated with the school environment, including the nutritional quality of foods sold or offered at school, administrative support, and foundational health programming prior to policy development. Staff identified the school as a role model for community members and as a key facilitator of policy implementation (for example, in leading health initiatives, providing a place for nutritious food and physical activity opportunities, and acting as a health resource for all community members). Barriers included inconsistency between staff members in policy implementation, uncertainty about staff members’ role in policy implementation, and lack of school communication with parents regarding the policy. One of the informative barriers from a First Nation perspective was the perceived misalignment of traditional foods, such as bannock or wild game, served at First Nation cultural events with federally derived nutrition standards that emphasize a low-fat diet. Results suggest strengthening school nutrition policy implementation by increasing staff nutrition education and certainty of their roles as policy facilitators, advocates, and enforcers; improving communication with families; having supportive school health programming; and ensuring the school, community, and home environment all reinforce healthy eating.