Rapid urbanization and climate change have intensified the urban heat island (UHI) effect, creating significant challenges for achieving thermal comfort in cities. As extreme heat events grow more frequent, urban greenery is increasingly recognized as a key strategy for outdoor cooling. However, the underlying mechanisms like shading, evapotranspiration, and wind modulation, remain inconsistently assessed across studies and highly sensitive to site conditions and research methods. To address this gap, we conducted a systematic review of 50 peer-reviewed articles, guided by the PRISMA 2020 protocol. We applied bibliometric analysis and thematic coding to extract and synthesize greenery-related indicators, including canopy cover, vegetation structure, spatial layout, and technological integration. This review introduces a five-part typology of strategies for enhancing thermal comfort through urban greenery: design configuration, site-specific planning, technological tools, community engagement, and performance monitoring. A structured quality assessment was applied to classify study reliability and confidence in reported outcomes. High-confidence studies combining empirical validation and thermal indices reported consistent ambient temperature reductions between 1.5 degrees C and 4.5 degrees C. Building on these findings, the study proposes a conceptual framework linking greenery inputs, environmental mediators, and contextual modifiers to thermal comfort outcomes. It also identifies equity gaps, particularly in underrepresented tropical and arid regions, and critiques the exclusion of non-open-access and grey literature as a limitation. This synthesis advances a more integrated, evidence-based foundation for climate-responsive urban design and offers practical guidance for policymakers, planners, and researchers committed to building resilient and equitable urban environments.