Sexual assertiveness - the tendency to take initiative and act independently regarding one’s own sexual desires and behavior - is shaped by gendered expectations that portray men as sexually assertive and women as submissive (i.e., traditional sexual script). Using dyadic data from 383 German couples, including heterosexual and LGBTQ partnerships, we tested competing explanations for sexual assertiveness: gender, heteronormativity, or experienced power within relationships. Multilevel analyses showed no support for gender or heteronormativity hypotheses: women and men reported similar levels of sexual assertiveness across couple types. In contrast, individuals with greater experienced power reported higher sexual assertiveness, a pattern consistent across heterosexual and LGBTQ couples. The strength of the power–assertiveness link varied across couples, being strongest in relationships with higher overall assertiveness. These findings advance theory by demonstrating that sexual assertiveness reflects experienced power rather than gender or heteronormativity, highlighting the importance of sociorelational characteristics in shaping sexual assertiveness.