The growing prevalence of polymer-based plastics in the environment is an imminent risk to the natural world. As an immediate consequence of this, extensive research has been launched over the course of the past few decades in an effort to reduce the damage that manmade plastics cause to the natural environment. The current study attempts to explore the biodegradability of polylactic acid (PLA), a bio-compatible plastic, by incorporating small amount of electron beam irradiated natural fibers (2 to 10%) derived from luffa cylindrica (LC) at varying irradiation doses (0.5 Gy, 1 Gy, and 2 Gy). Natural fiber surface treatment using electron beam irradiation is effective and environmentally friendly. The biodegradation of composites was studied for 90 days in sand, soil, compost, brackish water, fresh water, salt water, and bacterial and fungal conditions. Maximum decomposition was observed in the composite sample (PLA/10% wt of LC fiber at 2.0 Gy) at 15.42% and 4.73% in bacterial and soil environments. X-ray diffraction (XRD) and Raman spectroscopy validated the fiber and PLAs crystallinity and molecular interaction. The derivative thermo-gravimetric curve (DTGA) showed that electron beam irradiation removed moisture, hemicelluloses, and lignin from hydrophilic fibers. The incorporation of LC fibers into the bio-composites resulted in an increase in the glass transition temperature ( T g ), melting temperature ( T m ), and crystallization temperature ( T c ). Additionally, after LC fiber reinforcement, the composites’ dielectric properties were enhanced. Graphical Abstract