Reinforced concrete (RC) bridge columns often encounter combinations of loads including flexural, axial, shear, and torsional forces during seismic events, especially in the presence of geometric irregularities such as skewed or curved bridges, unequal spans, or varying column heights. Fibre-reinforced polymer (FRP) reinforcement offers a durable alternative to traditional steel bars in aggressive environments, given its corrosion resistance. Recent research has focused on the seismic behaviour of FRP-RC columns. Yet, existing seismic provisions for FRP-RC columns lean on modified steel-RC column models, overlooking the distinct behaviour of FRP-RC columns, particularly under varying concrete strength and combined loading, leading to suboptimal designs. This study experimentally and numerically investigated the seismic behaviour of circular glass FRP (GFRP)-RC columns. Fourteen large-scale GFRP-RC column-footing connections were constructed and tested under concurrent axial loading and quasi-static cyclic lateral drift reversals, inducing additional torsional effects. The effects of reinforcement type, torsion-to-bending moment ratio, transverse reinforcement ratio and configuration, longitudinal reinforcement ratio, and concrete compressive strength were investigated. The numerical phase involved constructing and validating a nonlinear finite-element model against experimental results, followed by a comprehensive parametric study using the validated models. The results showed that, with the same reinforcement ratio, the addition of torsion to cyclic bending and shear significantly altered the behaviour of the GFRP-RC columns in terms of mode of failure, drift capacity and stiffness degradation. Increasing transverse reinforcement ratio mitigated core damage and sustained torsion-induced tensile stresses. Adopting a spiral pitch equal to one-sixth of the effective core diameter of the column improved peak lateral load, torque, drift, and twist capacities. The use of GFRP discrete hoops with a lap splice length of 60 times hoop bar diameter is not recommended for columns subjected to seismic loading including torsional effects. Increasing the longitudinal reinforcement ratio enhanced lateral load, drift, and twist capacities. Furthermore, the validity of the North American design provisions predicting the torsional strength of GFRP-RC members subjected to combined seismic loading were examined. A change in the GFRP tensile stress limits provided in these provisions were proposed, which resulted in better predictions for the torque capacity of the tested columns.