In this study, elastic/plastic buckling analysis of thick skew plates subjected to uniaxial compression or biaxial compression/tension loading using the generalized differential quadrature method is presented for the first time. The governing differential equations are derived based on the incremental and deformation theories of plasticity and first-order shear deformation theory. The elastic/plastic behavior of the plates is described by the Ramberg–Osgood model. Generalized differential quadrature discretization rules in association with an exact coordinate transformation are simultaneously used to transform and discretize the equilibrium equations and the related boundary conditions. The results are compared with the previously published data to verify the established methodology and procedures. The effect of skew angle and thickness ratio on the convergence and accuracy of the method are studied. Moreover, the effects of aspect, loading and thickness ratios, skew angle, incremental, and deformation theories and different types of boundary conditions on the buckling coefficients are presented in detail. The results show that the difference between the incremental and deformation theories becomes greater with increasing thickness ratio and constraints at boundary conditions. Furthermore, the skew angle also has an important effect on differences between those theories.