Natural fibre-based polymer nanocomposites have played an essential role in many industry domains for four to five years because of their strong mechanical and physical qualities. The primary goal of this research is to establish the mechanical and morphological properties of nanocomposite materials in natural environments. Flax fibre was employed as a reinforcement, nanographene powder was used as a filler, and epoxy resin was used as a matrix material to achieve the goals above, keeping the following restrictions in mind: (i) fibre length (15, 30 and 45 mm), (ii) fibre content (10, 15 and 20 mm), and (iii) wt.% of nanofiller (2.5, 5 and 7.5 wt.%). The composite materials were laminated using the compression moulding process per the Taguchi L9 design. The mechanical characteristics of the material, such as flexural, tensile, and impact properties, were examined according to ASTM standards. The mechanical characteristics of combinations A2, B2, and C2 are the best when compared to other combinations. The graphene-based nanocomposites revealed that 2.5 wt.% graphene contributes 33.08% of mechanical properties, the 5 wt.% graphene contributes 36.4%, and the 7.5 wt.% graphene contributes 30.53%. Including 5 wt.% graphene content provides the highest mean values of mechanical strength like 36.59 MPa tensile, 40.25 MPa flexural, and 31.68 kg/m2 of impact. Scanning electron microscopy (SEM) images of the cracked specimens were used better to understand the failure process of composites during mechanical testing.