Pistachio green husk, an underutilized agricultural by-product with high potential, is often neglected in many regions. This study investigated the interactive effects of additives, particle size, and temperature on the mechanical and chemical properties of pellets produced from pistachio green husk waste for animal feed. Analysis of variance showed that temperature, additives, and particle size each had significant independent effects on pellet durability, maximum fracture force, fracture energy, and toughness. The most pronounced improvements in durability, maximum fracture force, fracture energy, and toughness were observed for the treatment combining 50% additives, an 80°C conditioning temperature, and a 0.5 mm particle size. Pellets produced at 80°C with 80% additives exhibited the largest reductions in phenolic compounds and tannin content—79% and 81%, respectively compared with unpelleted pistachio green husk. Additionally, an optimal treatment (70°C, 80% additives, 0.5 mm particle size) resulted in substantial decreases in acid detergent lignin (58%) and in acid detergent fiber and neutral detergent fiber (50% and 30%, respectively) relative to unprocessed (unpelleted) husk. These findings indicate that optimizing particle size, additive level, and processing temperature not only enhances the mechanical performance of pellets but also significantly reduces antinutritional factors, yielding economically attractive and more sustainable animal feed produced from agricultural waste.