This study proposed a newly built-up CFST column reinforced by diagonal props called a diagonal prop CFST column. Experiments were performed to investigate the response of the proposed column section subjected to axial compression. The CFST column behavior was presented using typical curves of load-deformation, load–strain, and load-carrying capacity. Further, the parametric analysis was performed to explore how changing the prop’s geometry and materials can affect its ultimate strength. The diagonal props inside the CFST columns controlled the steel tube from buckling throughout the height of the columns, which also made the concrete inside the tube more flexible. Under axial compression, it was found that a prop bar with a diameter of 8–16 mm makes the proposed CFST columns more conservative compared to the CFST columns without props. Also, an equation was developed to estimate the CFST column's ultimate strength under axial loading. The experimental results and the proposed equation were observed to be in good agreement with each other.