Sexual motivation, the interest in sexual activity, affects people's thinking, feeling, and behavior. Common scales used to assess sexual motivation suffer from drawbacks that limit their validity and applicability. We therefore developed and validated the Trait Sexual Motivation Scale (TSMS), a brief, theory-driven self-report scale, over the course of four preregistered studies (Ntotal = 2,083). Results indicated good model fit, high internal consistency and stability of the second-order (i.e., trait sexual motivation) and first-order (i.e., cognition, affect, behavior) factor scores, and scalar measurement invariance for gender and relationship status. The TSMS correlated as expected with sexual and non-sexual constructs and predicted sexual outcomes cross-sectionally and prospectively in everyday life. Overall, the TSMS emerged as an economical, reliable, and valid measure of sexual motivation.