This study examines the mechanical, water uptake, and soil degradation performance of pineapple leaf fiber (PALF) reinforced polypropylene (PP) composites subjected to gamma irradiation. Composites containing 40 wt.% PALF were fabricated through compression molding, and gamma doses ranging from 2.5 to 10 kGy were applied to evaluate radiation-induced modifications. Tensile, bending, and elongation properties were assessed using ASTM-standard procedures. Gamma irradiation influenced fiber–matrix interaction and produced noticeable variations in mechanical behavior. The tensile modulus improved at 7.5 kGy, whereas higher radiation levels caused a decline. Elongation at break showed a decreasing trend due to enhanced interfacial adhesion and restricted polymer mobility. Water absorption remained low (0.92–1.85%) since PP is hydrophobic, although minor uptake occurred through exposed fiber edges. Soil burial tests for four weeks demonstrated gradual weight loss (up to 8.12%), attributed to cellulose biodegradation, while PP exhibited limited deterioration. The composites preserved nearly half of their initial mechanical integrity after one month of soil exposure. The findings emphasize the future promise of PALF as an efficient reinforcement for PP and show that controlled gamma irradiation can fine-tune composite performance for sustainable engineering applications.