The current investigation focuses on developing composites by combining biodegradable and environmentally sustainable natural fibers with a thermoplastic matrix that can be recycled. Microwave-assisted compression molding (MACM) was used to create natural fiber composites of high-density polyethylene (HDPE) with a 15 wt% Ramie fiber content. The HDPE specimens were manufactured without any other modifications to observe the impact of reinforcing ramie fibers. The mechanical properties of the composite were assessed by tensile, flexural, impact, and hardness tests. Fractured surfaces were analyzed using scanning electron microscopy to identify the causes of failure. The HDPE/Ramie composites had an ultimate tensile strength (UTS) of 23.8 ± 0.3 MPa, which exceeded the UTS of pure HDPE (18.9 ± 0.4 MPa). HDPE/Ramie had a flexural strength of 20.3 ± 0.4 MPa, whereas plain HDPE had the lowest strength at 16.6 ± 0.7 MPa. The impact strength exhibited a comparable pattern, with the HDPE/ramie composite displaying the highest value at 35.2 KJ/m2, while plain HDPE followed at 23.7 KJ/m2. The hardness testing indicated that the HDPE/Ramie composite had a hardness that was 16.29% greater than plain HDPE. A computational study was conducted to create a model for accurately predicting the orthotropic properties of HDPE/Ramie composites. There is a notable consensus between computational and experimental studies. The new composite can be considered appropriate for various low-intensity uses, including roofing, automotive interior panels, and mobile covers. It has the potential to provide advantages in terms of decreasing carbon emissions.