Although Mental Health Literacy (MHL) has been a topic of substantial interest, measurement of this concept using a scale-based measure has been limited, including a lack of psychometric and methodologically robust scale-based measures of MHL. This study developed a new scale-based measure of MHL, the Mental Health Literacy Scale (MHLS), which assesses all attributes of MHL. Construction of the MHLS was done over three key stages, including measure development, pilot testing and assessment of psychometrics and methodological quality. The resulting measure is a 35 item, univariate scale that is easily administered and scored. Results showed significant differences in scores between mental health professionals and a community sample, as well as individuals with greater experience with mental health, and a significant positive relationship with help-seeking intentions. The MHLS also demonstrated good internal and test–retest reliability. Evaluation of the methodological quality of the MHLS indicated that it has substantial methodological advantages in comparison to existing scale-based measures of MHL. The MHLS can be used in assessing individual and population level differences in MHL and in determining the impact of programmes designed to improve MHL.