This study investigates the local buckling (LB) behaviour of pultruded glass-fibre reinforced polymer (pGFRP) columns through both experimental and computational approaches. The experimental program focused on slender wide-section members, to clearly capture LB modes. Digital Image Correlation (DIC) was employed to monitor the strain distribution during the post-critical phase, up to failure. Additionally, prior to the experiments, high-precision measurements of initial geometrical imperfection (GI) of the tested specimens were conducted using a 3D Coordinate Measuring Machine (CMM). Material properties were also characterized via coupon and full-section tests. A shell-based finite element model (FEM), incorporating Hashin’s criteria for damage initiation and propagation, along with nonlinear geometric analysis accounting for measured imperfections, was developed to provide further insights into post-buckling behaviour. Future research will utilize these experimental results to contribute to a comprehensive database aimed at developing an accurate and practical design procedure for pGFRP structures following the Direct Strength Method (DSM). Finally, the proposed shell-based FEM can be used to develop parametric studies on the ultimate strength of pGFRP columns (other than those used to calibrate the DSM curves), allowing to assess the DSM curves for a wide range of geometries (slenderness values) not currently available in the market.