Children begin pre-school with varying levels of school readiness. Those children who enter pre-school with better foundational mathematics skills are more likely to succeed in school than those who do not. This initial variation in early mathematics suggests that experiences outside of the school setting, namely the home environment, may support learning and development. This study aims to systematically develop a comprehensive home mathematics environment questionnaire that reliably assesses the experiences of pre-school children (i.e., 3–5-year-olds) following recent recognised scale development and validation methods. Four studies were used to develop and validate the Pre-school Home Mathematics Questionnaire (PHMQ). Study 1 focused on 1) item generation through individual, in-depth interviews with parents of young children and 2) identifying previous questions from other home mathematics environment (HME) questionnaires to be incorporated into the PHMQ. Study 2 involved questionnaire refinement and was used to assess the psychometric properties of the new measure while addressing construct validity (i.e., factor structure and scale score reliability). Study 3 assessed content and criterion validity of the scale. Finally, Study 4 focused on construct validity through confirmatory factor analysis. Overall, the four studies demonstrate construct, content, and criterion validity. Hence, the newly developed PHMQ satisfies the American Psychological Association (APA) standards for psychometric adequacy.