Background/Objectives Despite substantial evidence documenting weight stigma toward people with higher body weight, international comparative studies are lacking in this field. The few studies that have compared weight stigma across different countries focus on explicit weight-biased attitudes rather than people's experiences of weight stigma. The present study conducted a multinational systematic comparison of weight stigma in six countries to assess experiences and interpersonal sources of weight stigma. Subjects/Methods Adults (N = 13,996) enrolled in WW International (formerly Weight Watchers), residing in Australia, Canada, France, Germany, the UK, and the US completed identical online anonymous surveys in the dominant language for their country. Surveys assessed their history of experiencing weight stigma, the onset of stigmatizing experiences and associated distress from stigma in different time periods, and interpersonal sources of weight stigma. Results More than half of participants (55.6-61.3%) across countries reported experiencing weight stigma. Participants with higher BMI were significantly more likely to report weight-stigmatizing experiences than individuals with lower BMI. In all countries, weight stigma experiences were most frequent in childhood and adolescence, with associated distress highest during these time periods. Participants in Germany reported a higher frequency of weight stigma across their whole life, but lower distress associated with stigmatizing experiences, compared to participants in the other five countries. High percentages of participants in each country experienced weight stigma from family members (76.0-87.8%), classmates (72.0-80.9%), doctors (62.6-73.5%), co-workers (54.1-61.7%), and friends (48.8-66.2%). Conclusions Weight stigma is prevalent for adults actively engaged in weight management across different Western countries. There were more similarities than differences in the nature, frequency, and interpersonal sources of people's experiences of weight stigma across the six countries in this study. Findings underscore the need for multinational initiatives to address weight stigma and interventions to support individuals engaged in weight management who experience weight mistreatment.