Purpose of the study: The study investigated the effect of sustainable procurement practices on supply chain performance among tier-one supermarkets in Kiambu County, Kenya. It focused on four practices-green procurement, ethical sourcing, supplier selection criteria, and procurement governance-and how they influence lead time efficiency, inventory management, product quality, and cost efficiency. Problem Statement: Despite growing awareness of sustainability, many supermarkets in Kiambu continue to face high operational costs, unreliable suppliers, and weak procurement systems. These challenges undermine competitiveness, particularly in a fast-expanding retail environment where consumer expectations for quality, efficiency, and affordability are rising. Methodology: The study adopted a descriptive research design targeting 106 heads of procurement. Using a census approach, 86 valid responses were obtained, representing an 81.13% response rate. Primary data were collected through structured questionnaires, tested for validity and reliability, and analyzed using descriptive and inferential statistics, including correlation and regression techniques. Findings: The study revealed that all four sustainable procurement practices had significant positive effects on supply chain performance. Supplier selection criteria emerged as the most influential predictor, while green procurement enhanced cost efficiency and waste reduction.Ethical sourcing improved supplier dependability, and procurement governance strengthened accountability and transparency. Conclusion: The study concludes that procurement is not merely administrative but a strategic driver of supply chain performance. Recommendations: The study recommends that supermarkets institutionalize green procurement policies emphasizing energy efficiency and waste reduction, adopt mandatory ethical sourcing audits, implement rigorous supplier selection frameworks, and strengthen governance through automation, auditing, and transparent reporting. Embedding sustainability in procurement systems will enhance resilience, efficiency, and long-term competitive advantage in Kenya’s dynamic retail sector.