This experimental study investigates the axial compressive behavior of concrete-filled double-skin tubular (CFDST) stub columns strengthened with a single layer of glass fiber-reinforced polymer (GFRP). six specimens were tested across two groups—reference (CF0) and strengthened (CF1)—to evaluate the effects of external GFRP confinement on ultimate load-carrying capacity, secant stiffness, ductility, failure mechanisms, and post-peak response. The results indicate that the GFRP layer effectively delays local buckling of the outer steel tube and enhances the composite interaction between the steel tubes and the concrete core. Based on experimental data, the strengthened specimens exhibited an average increase of 10.94% in ultimate load-carrying capacity, 7% in ductility, 26% increase in energy absorption and 3.8% in secant stiffness compared to the control group. Failure in the strengthened samples initiated with the sudden rupture of the GFRP layer, immediately followed by the development of buckling waves in the outer steel tube; this highlights the effective confinement provided prior to fiber fracture. Additionally, a Performance Enhancement Index (PEI) was introduced to simultaneously quantify improvements in various mechanical parameters. The findings confirm that a single GFRP layer offers an efficient strategy for enhancing the axial performance of CFDST columns, providing valuable practical data for optimal design and retrofitting of composite sections in structural engineering.