The article delves into the promising role of hydrogen in mitigating emissions in the energy industry by exploring sustainable production methods. Specifically, it highlights the challenges in storing and transporting hydrogen despite its environmental benefits. The study conducted a detailed techno-economic analysis to evaluate onsite hydrogen production through ammonia decomposition using the heat recovered from exhaust gas generated by hydrogen-fueled gas turbines. By utilizing Aspen Plus simulation software and economic evaluation tools, the research compared the cost-effectiveness of this approach with traditional methods. The analysis revealed a levelised cost of hydrogen (LCOH) at 5.64 USD/kg, showcasing a 10.6% decrease compared to conventional techniques that rely on a furnace to heat ammonia. The primary cost driver identified was the ammonia feed cost, which accounted for up to 99% of the LCOH. The study also underscored the sensitivity of LCOH to the price of ammonia, suggesting the necessity of reducing green and blue ammonia costs for long-term viability. The research findings support the economic feasibility of ammonia decomposition with heat recovery for onsite hydrogen production, signaling a significant advancement in sustainable energy practices.