This study examines the impact of substrate type, composition, and addition of gelatin solid waste (GSW) on bio-hydrogen production from organic waste by dark fermentation, a process known for its ability to sustainably convert organic materials into hydrogen without the need for light energy. Peels from fruits (FPs), vegetables (VPs), and a combination of the two (MFVPs) were used in a series of batch experiments to find the best substrate producing the highest bio-hydrogen. According to the results, the most efficient combination of 25% pea, 25% tomato, 25% banana, and 25% orange peels produced the highest HY of (73.16 ± 9.5 ml/g COD), VHP of (2.48 ± 0.33 L/L), and HC of (64.7 ± 3.7%), respectively. Then, an additional batch of experiments was conducted to investigate the effect of GSW addition on H2 production and fermentation efficiency. Therefore, different concentrations of GSW (1, 2, 4, 6, 8, and 10 g) were added to this optimal mixture, and the findings showed that the optimal dose of GSW was 2 g; this dose considerably shortened the time to peak hydrogen production from 28 to 18 hrs. and boosted cumulative hydrogen production (CHP) by almost 60%. These results highlight that substrate diversification and nutrient supplementation significantly increased organic waste fermentation and biohydrogen production. The broader implications of this study include potential applications in industrial waste management and renewable energy sectors, where optimizing fermentation processes could reduce waste while providing a cleaner energy source