This study of the determinants of the choice to combine management and control functions, and then the impact of this choice on the performance of large French companies with monistic structures, relies on agency, entrenchment, stewardship, and substitution theories. The results, based on data from 2011–2021, show that the decision to combine functions depends on the human capital of the board of directors and the CEO’s seniority; independent directors and the proportion of capital held by the executive instead favor separation. This choice has no influence on the company's financial performance. However, when the proportion of independent directors is high or the board possesses a high level of human capital, combining the management and control functions benefits the company's financial performance.