We examine the impact of CEO duality on firm performance using the life-cycle theory approach. The data is balanced and covers over the period 2012–2018 for 442 publicly listed firms in Vietnam. The findings from system generalized method of moments (GMM) method indicate that CEO duality had a positive effect on firm performance in growth stage and had a negative effect on the mature stage of the firm’s life-cycle. These results are supported by stewardship theory which argues that CEO duality may be good for firm performance in the growth stage due to the unity of presented command. In contrast, agency theory shows CEO duality is bad for firm performance in the maturing stage since it compromises the monitoring and controls the behavior of the CEO. Also, this study shows that there was a difference between state shareholders and director from outside of the company affecting the firm performance.