Public health campaigns on substance use and physical activity aid disease prevention. This review examines how process evaluations are conducted in substance use and physical activity campaigns, focusing on methodologies, theoretical frameworks, implementation quality, fidelity, reach, and delivery. Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, a comprehensive literature search was conducted across PubMed, PsycINFO, Web of Science, Scopus, ProQuest, and Google Scholar from 1990 up to April 2025. Eligible studies included randomized controlled trials, quasi-experimental, and observational designs involving adult human participants and reporting process or implementation evaluation components. Twenty-one studies met inclusion criteria. A one-step forward citation analysis was performed using the bibliometrix package in R. Findings revealed that 62% of studies reported process evaluation components, with 52% employing mixed-method approaches. Commonly cited theoretical frameworks included the Transtheoretical Model, Theory of Planned Behaviour, and Social Cognitive Theory. Only 20% of studies explicitly defined process evaluation objectives, and few translated findings into actionable implementation adaptations. Bibliometric analysis indicated influence across 373 publications, primarily from the United States, Australia, and Canada. Overall, process evaluation in public health campaigns remain inconsistent. To enhance the quality and utility of such evaluations, greater theoretical integration, improved methodological transparency, and the use of standardized assessment tools are recommended.