Abstarct: Today, the use of nanocomposites has expanded due to its favorable mechanical and thermal properties in many industries, including aerospace, medicine, military, etc. Therefore, in the present numerical study, the thermomechanical buckling and post-buckling of functionally graded plates with a matrix of isotropic polymer (diglycidyl ether bisphenol A) and reinforced with graphene platelets (GPLs) under simply supported and clamped boundary conditions has been investigated. The plates are subjected to uniform temperature changes and in-plate forces. In these multilxayer plates, the thickness of all laxyers is the same, and the GPL weight fraction may have a laxyer-wise variation across the plate thickness. The plates are reinforced with two functionally graded (X and O) and uniform (U) distributions. The effective Young’s modulus of the plates is calculated using the modified Halpin-Tsai micromechanical model, and also the mixing law is used to obtain the equivalent properties of the composites. Within the frxamework of the first-order shear deformation theory (FSDT), the nonlinear governing equations are derived by applying the principle of virtual displacements and then solved by using a differential quadrature-baxsed (DQ) iteration technique, calculate the critical buckling temperatures and loads, and determine the thermal and mechanical post-buckling paths. By comparing the results of the present study with other sources, the accuracy and efficiency of the steps taken, have been confirmed. The effect of aspect ratio, width-to-thickness ratio and GLP weight fraction, boundary conditions, on buckling temperature and post-buckling equilibrium paths of the plates have been investigated. The results show the functionally graded distribution of the GLPs does not necessarily improve the buckling strength of the plates. In the functionally graded distribution of GLPs as X, the plate’s resistance to thermal and mechanical buckling increases, while in the distribution of GPL as O, the buckling strength of the plates decreases. Plates with GLPs distribution of X, U and O respectively have the highest buckling load, buckling temperature and post-buckling equilibrium path.