Attitudes is a key help-seeking construct that influences treatment seeking behavior via intention to seek help, per the theory of planned behavior (TPB). This article presents the development and psychometric evaluation of the Mental Help Seeking Attitudes Scale (MHSAS), designed to measure respondents’ overall evaluation (unfavorable vs. favorable) of their seeking help from a mental health professional. In Study 1 (N = 857 United States adults), exploratory factor analysis (EFA), confirmatory factor analysis (CFA), and item response theory (IRT) analysis were used to identify an optimal set of 9 items that demonstrated initial evidence of internal consistency, unidimensionality, and strong measurement equivalence/invariance (ME/I) across gender, past help-seeking experience, and psychological distress. Initial convergent evidence of validity was demonstrated via theoretically anticipated relationships between the MHSAS and key variables in the help-seeking nomological network (e.g., subjective norms, perceived behavioral control, intention, public stigma, self-stigma, anticipated risks and benefits, gender, previous help seeking). Initial incremental evidence of validity was demonstrated when the MHSAS demonstrated the ability to account for unique variance in help-seeking intention, beyond that accounted for by the Attitudes Toward Seeking Professional Psychological Help—Short Form scale (ATSPPH-SF) and the Psychological Openness subscale of the Inventory of Attitudes Toward Seeking Mental Health Services (IASMHS-PO). Study 2 (N = 207 United States adults at Times 1 and 2) provided initial evidence of test–retest reliability over a 3-week period. The MHSAS offers mental health professionals a new tool for measuring attitudes that may avoid limitations of current help seeking-attitudes measures (e.g., construct-irrelevant variance).