Objective <p>Though sufficient and stable funds are critical to effective public health systems, existing literature on public health system financing is limited. This study aimed to address this gap by uncovering the salient factors influencing public health system financial decision-making.</p> Methods <p>We conducted a qualitative case study of public health system financing in British Columbia, consisting of a jurisdictional review of academic and grey literature, and semi-structured interviews with 14 participants influential in public health budget-setting. Taking an inductive analytical approach, we constructed a conceptual model of the political, structural, and external factors influencing public health funding trends. Building on insight from participants, we identified promising policy considerations for improving the sustainability of public health funding.</p> Results <p>Participants identified that external factors such as public health crises and major sociopolitical events create windows of opportunity for investments or cuts. They reported that structurally separating public health budgets from other health service budgets seems to protect public health funding. Political priorities of top decision-makers were highlighted as the most influential political factor, though advocacy has been successful in bringing public health issues onto the political agenda. Strong relationships between public health actors and decision-makers such as senior executives are seen as important for promoting investment in public health programs.</p> Conclusion <p>This study sheds light on some of the possible policy strategies for sustaining public health funding, such as inclusion of public health experts in financial decision-making and developing public health performance indicators, which may inform current public health system strengthening efforts.</p>