This paper offers a novel theoretical account of why and when top management team (TMT) gender diversity lends strategic advantage. Building on social role theory, we develop a moderated-mediation model showing: a) TMT psychological safety mediates the effect of TMT gender diversity on firm ambidextrous strategic orientation (ASO) (why) and b) firm slack moderates this mediated effect (when). We tested our model in the context of Chinese high-tech small- and medium-sized enterprises. After confirming gender differences in social role-based proclivities at the TMT level, a multi-wave survey study of 373 members from 120 TMTs showed that TMT gender diversity positively affects ASO via TMT psychological safety, and this mediated effect is stronger when firm slack is lower than higher. We further interviewed 23 top managers to supplement key quantitative results. Our study advances upper echelons research on TMT gender diversity in two ways. First, it highlights the gender-specific interpersonal benefit of TMT gender diversity, which is markedly distinct from the cognitive-variety argument associated generically with TMT demographic diversity. Second, it considers both men and women in TMTs in a more balanced manner, thereby offering an alternative account to the female-focused theorization of the positive strategic implications of TMT gender diversity.