BACKGROUND:
Public health challenges are increasingly complex, shaped by social, structural, and environmental determinants that demand robust theoretical grounding and methodological rigor. While empirical evidence underpins effective public health action, gaps persist between theory, research design, and real-world application. Strengthening the integration of public health theories and innovative research methods is critical to generating actionable evidence capable of informing equitable and sustainable health interventions.

METHODS:
This paper presents a narrative synthesis of foundational and contemporary public health theories alongside established and emerging research methodologies. Peer-reviewed literature, methodological frameworks, and global public health guidance were examined to assess how theory informs study design, data collection, analysis, and knowledge translation. Emphasis was placed on mixed-methods approaches, participatory research, and systems-based methodologies.

RESULTS:
Findings demonstrate that theory-driven research designs enhance explanatory power, improve intervention fidelity, and strengthen causal inference in public health studies. The use of mixed-methods and participatory approaches was associated with greater contextual relevance and improved uptake of findings by policymakers and communities. Systems-oriented and implementation science methods further supported scalability and sustainability of public health interventions.

DISCUSSION:
The results highlight the necessity of moving beyond descriptive research toward analytically rigorous, theory-informed methodologies that reflect the complexity of population health. Integrating social, behavioral, and systems theories with innovative research methods enables more precise identification of mechanisms driving health outcomes and inequities. Impact on Practice This work provides researchers, practitioners, and decision-makers with evidence-informed guidance on strengthening the theoretical and methodological foundations of public health research. Advancing theory-driven, methodologically robust research is essential to improving evidence quality, informing policy, and achieving meaningful population health impact.