The non-linear in-plane primary resonance of functionally graded porous (FGP) arches made of graphene platelet reinforced composites (GPLRC) under a transverse harmonic excitation is investigated in this paper. Equations of motion are established considering the force and bending moment equilibrium conditions. By utilizing an incremental harmonic balance (IHB) technique, the frequency response features are obtained. Comprehensive parametric studies are then carried out, particular focus is paid to the cases of porosity distribution patterns, load amplitudes, porosity coefficient, damping ratio on the frequency response characteristic. It is found that the increasing porosity coefficient significantly exacerbates the left-inclined softening behaviors of the frequency response curves. On the contrary, the left-inclined effect continues to weaken as the GPL weight fraction gradually grows.