Continental rift basins host prolific hydrocarbon resources; however, their tight sandstone reservoirs often undergo complex diagenetic modifications, resulting in significant heterogeneity and uncertainty in reservoir predictions. While the processes of compaction, cementation, and dissolution have been extensively documented, the influence of volcaniclastic input on diagenetic pathways and pore-system evolution remains inadequately constrained, which limits our understanding of reservoir quality in volcanic-influenced settings. In this study, we integrated core observations, blue-epoxy–impregnated thin sections, cathodoluminescence (CL), SEM–EDS, XRD, NMR, and micro-CT analyses to investigate the Shahezi Formation sandstones from on the northern slope of the Lishu Fault Depression in the Songliao Basin. We identified five diagenetic facies types: (1) tightly cemented (DFT-Ⅰ), (2) moderately compacted with carbonate-cement dissolution (DFT-Ⅱ), (3) moderately compacted with unstable-grain dissolution (DFT-Ⅲ), (4) strongly compacted and densely cemented (DFT-Ⅳ), and (5) strongly compacted with intergranular dissolution (DFT-Ⅴ). Quantitative pore-network characterization reveals that the dissolution of volcaniclastic grains and associated cements significantly enhanced porosity and connectivity in DFT-Ⅱ and DFT-Ⅴ, whereas DFT-I and DFT-Ⅳ experienced intense compaction and cementation, resulting in ultra-tight intervals. Illite-dominated clay assemblages found at burial depths greater than 4000 m and temperatures exceeding 160 °C indicate a late, high-temperature diagenetic stage. These findings demonstrate that volcaniclastic input plays a critical role in diagenetic evolution and reservoir heterogeneity in tight rift-basin sandstones. By incorporating the effects of volcaniclastic materials into diagenetic facies classification, we can improve reservoir quality predictions for the Shahezi Formation and establish a transferable framework applicable to tight sandstone systems across continental rift basins globally.