The large-scale use of non-biodegradable materials, mainly comprising plastics, has raised serious environmental concerns for their viable alternatives. However, most of the biocomposites, including PLA-based matrix material, exhibit shortcomings in mechanical and thermal properties, thus posing serious barriers to their applications. Dealing with such challenges, the present work is related to the additive manufacture of biocomposites using poly(lactic) acid (PLA) reinforced with sapodilla seed shell (SSS) particulates through a fused deposition method technique. PLA was mixed with different concentrations of SSS fillers such as 5 wt.%, 10 wt.%, 15 wt.%, 20 wt.%, and 25 wt.%. PLA and SSS were extruded into filaments used for 3D printing. The experimental results reported an improvement in tensile and flexural strength; in particular, the composites showed tensile and flexural strengths around 25.5 and 49.46 MPa, respectively, which is an increase of about 51.25% and 27.6% as compared to the PLA matrix. However, the addition of SSS fillers did not have any significant influence on impact energy absorption. Thermal stability was checked using thermogravimetric analysis, while its char residue increased from 1.15% to 2.59% in the composites, compared to pure PLA at 0.64%. These results clearly indicate that SSS fillers can overcome the inherent weaknesses of PLA, offering a promising solution toward lightweight and environmentally sustainable applications in additive manufacturing, such as biodegradable packaging materials and lightweight automotive interior components.