Background Young carers (YC) and young adult carers (YAC) have become of interest in research and practice. The 18-item Multidimensional Assessment of Caring Activities for Young Carers (MACA-YC18) was developed for identifying the extent and nature of caring activities across six domains: domestic chores, household management, financial/practical help, personal care, emotional care, and sibling care. The aim of this research was to investigate the psychometric properties of the French version of the MACA-YC18. Methods Two quantitative studies were conducted in a general population among adolescents and young adults. The sample was composed of 2688 adolescents (Mage = 16.08; SDage = 0.98; 60.60% girls) in Study 1 and 1192 young adults (Mage = 20.52; SDage = 1.89; 78.27% girls) in Study 2. The psychometric properties were examined via construct validity through internal consistencies, confirmatory factorial analysis, and invariance measurement regarding: gender (girls vs. boys), having a sick/disabled relative (having vs. not), relative's type of illness/disability (physical illness vs. mental illness vs. other illnesses/disabilities), providing support to a sick/disabled relative (providing vs. not), and living arrangement (with family vs. not). Results In both studies, internal consistencies were in line with those reported in the literature, the 6-factor structure was confirmed, and strict invariances were highlighted. Conclusions Results show that the French version of the MACA-YC18 has good psychometric properties regarding construct validity not only among adolescents but also among young adults. This instrument appears to be a relevant screening tool for identifying and characterizing young carers in the general population.