Sustainable drilling practices have become increasingly important as the oil and gas sector seeks to reduce environmental impact while maintaining operational performance. Fluid loss during drilling operations remains a persistent challenge, traditionally mitigated using synthetic additives associated with environmental and economic concerns. This study presents the first systematic evaluation of rambutan peel powder (RPP), an agricultural waste material rich in cellulose and bioactive polysaccharides, as a sustainable fluid loss control additive for water-based drilling muds. Rambutan peels were processed into fine powder and incorporated into base mud formulations at loadings ranging from 0.0 to 10.0 lb/bbl. Rheological properties, including apparent viscosity, plastic viscosity, gel strength, and yield point, were measured using a rotational viscometer, while filtration behavior and mud cake thickness were assessed through standard API tests. Results show that RPP enhances rheological performance by improving suspension stability and cuttings carrying capacity without inducing excessive viscosity. At the optimized loading of 4.70 lb/bbl, fluid loss decreased from 15.00 mL to 9.48 mL, corresponding to a 36.80% reduction, while mud cake thickness was reduced from 2.00 mm to 0.54 mm, representing a 73.00% reduction. The optimized formulation satisfied all API RP 13B-1 rheological and filtration requirements and performed comparably or better than previously reported agro-waste-based additives. These findings demonstrate that RPP is a viable, sustainable, and cost-effective alternative to conventional drilling fluid additives, supporting waste valorization and circular resource use while maintaining technical performance.