This work investigates the influence of graphene nanoplatelets (GNP) reinforcement on large amplitude vibrations for functionally graded (FG) poroelastic plates with initial geometric imperfection. By using continuous functions, the pore size and density are changed both symmetrically and asymmetrically along the thickness direction of the plate. The Halpin–Tsai and Voigt models are used, respectively, to determine the mass density and elastic modulus of the GNP-reinforced metal matrix, which are the effective material properties. Constitutive relations for the plates are established utilizing Biot's theory of linear poroelasticity. The Lagrange equation is employed to derive the nonlinear governing equations based on von Kármán nonlinearity and Kant’s higher order shear deformation plate theory (HSDT). The nonlinear natural frequency is accessed using a direct iterative approach followed by the finite element method. The influence of parameters such as porosity index, weight fraction of GNP, imperfection amplitude, and others is presented.