Corporate Sustainability Impact Assessment (SIA) has gained prominence as firms face increasing pressure to demonstrate measurable environmental, social, and economic impacts beyond disclosure. However, corporate SIA research remains fragmented, methodologically heterogeneous, and difficult to operationalise. This study systematically reviews methodological developments in corporate SIA through a Triple Bottom Line (TBL) lens, integrating bibliometric analysis with a Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)-based qualitative systematic literature review. Using the Theory–Context–Characteristics–Methodology (TCCM) framework, the study analyses 303 articles for bibliometric mapping and 67 peer-reviewed studies (2015–2025) for in-depth synthesis. Findings reveal a strong methodological dominance of multi-criteria decision-making approaches (≈55% of studies), a pronounced focus on supply-chain contexts, and growing thematic convergence between SIA and sustainability disclosure frameworks, though methodological integration remains limited. Indicator synthesis shows that stakeholder-prioritised weights are distributed almost evenly across the three TBL pillars, with a slight economic emphasis; the most heavily weighted indicator groups—greenhouse gas emissions/climate change, pollution and waste management; green management and circularity; and operational and process efficiency—each span all three pillars. By consolidating heterogeneous indicator sets and introducing a study-specific normalised weighting approach, this review provides a preliminary integrative reference for simplifying early-stage SIA and enhancing cross-study comparability. The findings support research and practice aimed at strengthening accounting and modelling phases of SIA and linking sustainability implementation to measurable outcomes.