The most crucial question in strategic management is the role of the top management team (TMT) in a company’s overall success. Empirical studies support the thesis that the TMT plays an important role in defining companies’ outputs, thereby focusing on TMT structure. The research question of this paper is as follows: What is the impact of TMT heterogeneity on large companies’ performance in Croatia? The authors employed a secondary quantitative approach. A panel analysis was conducted from 2015–2020. The research included 62 large companies that met the requirements. The results indicated a positive impact of gender and cultural heterogeneity on companies’ performance, as measured by return on assets (ROA). In the return on sale (ROS) model, a positive impact of TMT heterogeneity is not indicated. This paper contributes by identifying the TMT structure from heterogeneous aspects in Croatia and analysing the impact of heterogeneity on companies’ performance in line with the recommendations for defining the TMT structure.