The majority of studies examining discrimination in the asexual population adapted existing measures intended for lesbian, gay, and bisexual (LGB) people. While these studies examined overlapping experiences of discrimination between asexual and LGB individuals, they failed to assess facets of minority stress unique to asexual people. Asexuality is defined as the lack of, or little, sexual attraction towards others. The goal of the current study was to develop the Asexual Minority Stress Scale (AMSS), a validated self-report measure that assesses minority stress factors experienced by the asexual population. The methodology was guided by phenomenological theory and the minority stress model. The study used an exploratory sequential design. Participants (n = 721) completed an intake survey, and six researchers conducted interviews with 23 asexual participants. A thematic analysis guided item development for the preliminary AMSS. In Study 2, data (n = 896, nasexual = 666) were analyzed using Item Response Theory (IRT) with the 2-parameter logistic and nominal response models to guide item retention and modification. The finalized AMSS comprised 49 items with four subscales (Distal Stressors, Proximal Stressors, Coping Factors, and Protective Factors). Study 3 involved examining the psychometric properties of the AMSS using IRT, validity analyses, and the assessment of several exploratory hypotheses. The AMSS had high reliability, content validity, and known-groups validity, excellent convergent validity for the Distal and Proximal Stressors subscales, and excellent incremental validity for the Coping Mechanisms and Protective Factors subscales. The AMSS is the first validated instrument for the asexual population developed using IRT and provides a comprehensive assessment of minority stress factors that impact disparate health outcomes for asexual people within the minority stress model.