The purpose of this research is to examine the consequences of top management team (TMT) internationalization: why and under what conditions can TMT nationality diversity be beneficial? On the basis of the upper echelons theory from the strategic leadership literature, the relationship between the TMT nationality diversity and firm performance in the strategic context of firm internationalization is investigated in moderated multiple regressions models (MMR) for a sample of Dutch, Swiss, and UK companies. The study findings suggest that the TMT nationality diversity becomes advantageous only in firms with high degree of internationalization. Companies have to be strongly committed to foreign markets so that the benefits of the TMT nationality diversity can materialize. The arising managerial implication is that the TMT nationality diversity can be a powerful tool in building a firm’s competitive advantage, provided that companies are strongly exposed to the international environment. The study also provides corroborative evidence that the search for moderating and mediating variables in the TMT demography research represents a step in the right direction.