Indigenous people continue to experience the negative effects of colonialism and related prejudice, discrimination, and racism. I investigated whether knowing an Indigenous language may protect Indigenous people from such harmful experiences. I hypothesized that Indigenous people who speak an Indigenous language would experience better mental health and that both belongingness and collective self-esteem would mediate this relationship. I used statistical mediation to assess these hypotheses with the Statistics Canada 2017 Aboriginal Peoples Survey (n = 19,509). Unexpectedly, knowing an Indigenous language had a significant and negative effect on mental health. Respondents who spoke an Indigenous language perceived their mental health as poorer. As hypothesized, knowing an Indigenous language had significant and positive indirect effects on mental health via both belongingness and collective self-esteem. Respondents who spoke an Indigenous language felt they belonged more and better about their Indigenous community. These results imply that learning an Indigenous language may be one effective “treatment” to improve Indigenous peoples’ mental health by fostering feelings of belongingness and collective self-esteem. The results are, however, based on correlational evidence among one-item measures, but it is not possible to ethically manipulate exposure to language or randomly assign people to learn a language. While acknowledging this design limitation, I explain the implications of these findings for language programming revitalization and mental health intervention.