The research aims to investigate the features of a dual-fuel mode diesel engine that runs on hydrogen gas and sapota seed biodiesel (SSB) blend. Using gaseous hydrogen in diesel engines is a practical solution for enhancing energy efficiency and reducing emissions. The use of sapota fruit waste seeds as a new and innovative source to produce biodiesel has been recognized. It is essential to mention that sapota seeds are only used for sowing purposes other than those considered wasteful. A comprehensive review of earlier research indicates that this study, which uses an SSB blend in addition to hydrogen in dual-fuel operation, is essential. The primary objective of this research is to analyze the impact of hydrogen in SSB dual-fuel mode in single-cylinder diesel engines. Hydrogen was introduced into the intake manifold via a port fuel injector at flow rates of 3 and 6 liters per minute (LPM), with SSB as the fuel. The hydrogen energy share for 3 LPM and 6 LPM at maximum brake power (BP) conditions is 16.17% and 31.07%, respectively. The results revealed that hydrogen induction 3 LPM and 6 LPM increased cylinder pressure by 17.26% and 21.03%, heat release rate (HRR) by 43.91% and 56.13%, brake thermal efficiency (BTE) by 6.29% and 14.62%, and decreased brake specific energy consumption (BSEC) by 21.73% and 39.13% than diesel at maximum BP. Moreover, hydrogen 3 LPM and 6 LPM reduced carbon dioxide (CO₂), carbon monoxide (CO), hydrocarbon (HC), and smoke emissions by 18.61% and 28.26%, 49.68% and 77.20%, 63.01% and 83.28% and 23.24% and 34.63% than diesel at maximum BP. Oxides of nitrogen (NOx) emissions were increased by 2.84% in biodiesel when compared to diesel; however, when hydrogen was added, NOx emissions increased by 9.40% and 16.15% compared to diesel at maximum BP. This study found that adding hydrogen to SSB increased BTE and decreased emissions with slightly increased NOx emissions. This research concluded that biodiesel and hydrogen induction can substitute diesel fuel in diesel engines.