Barite sag remains a persistent challenge in water-based drilling fluids, particularly in high-pressure, high-temperature and deviated wellbores where density variations can compromise well control, hole cleaning, well stability and operational safety. Conventional weighting materials often fail to maintain suspension stability under such demanding conditions, highlighting the need for anti-sag solutions. This study presents a systematic evaluation of in-house synthesized barite nanoparticles (26.9–63.2 nm) manufactured using ball milling and incorporated into drilling fluids at concentrations of 0%, 3%, and 5% across densities of 9, 12, and 15 ppg. Using standardized API procedures, the fluids were assessed for rheology, filtration behavior, and sag tendency under both dynamic and static HPHT conditions to mimic realistic drilling environments. Results show that a 5% nanoparticle concentration significantly enhances drilling fluid performance, improving plastic viscosity (up to 50%), yield point (up to 51%), and gel strength (up to 80%), while also reducing fluid loss by 9–10% and mud cake thickness by up to 16%. Moreover, barite sag was substantially mitigated, with dynamic sag reductions of 10–50% and static sag reductions of up to 21% in inclined HPHT conditions. The novelty of this work lies in the comprehensive testing approach, from a practical perspective, covering the effect of an engineered barite nanoparticle to demonstrate a scalable and practical method to enhance sag resistance, suspension stability, and overall drilling efficiency.