Culture plays a crucial role in shaping how people perceive, interpret, and navigate psychological suffering. This dissertation examines cultural variations in mental health beliefs within Japan and Canada, utilizing two mixed-methods research designs. The overarching objective is to engage in interdisciplinary and culturally grounded research practices, driven by the need to address the lack of diversity, inclusion, and global perspectives in psychological science, commonly referred to as the “WEIRD” problem. These research practices entail critically reflecting on the generalizability of Western biomedical models, conducting literature reviews in Japanese, and fostering collaborations with Japanese researchers. Manuscript 1 examines the differences in causal and help-seeking beliefs about mental illnesses between Japanese and Euro-Canadian students. In this study, content analysis revealed themes related to social-contextualization and unique cultural perspectives, such as filial piety and resting. Statistical analysis showed group differences in the endorsement of explanatory models across various conditions, including depression, autism spectrum disorder, schizophrenia, alcohol use disorder, and hikikomori. Overall, Japanese students tended to psychologize and recommend social support, whereas Euro-Canadian students tended to medicalize and recommend medication and self-care. Manuscripts 2 and 3 apply cultural consensus theory to explore shared beliefs about mental health, depression, and therapeutic alliance among Japanese clinical psychologists. Using a two-phase sequential mixed-methods design, cultural domain analysis identified salient terms reflecting mental health issues and changes in licensure within Japan’s socio-cultural and historical context. Cultural consensus analysis demonstrated shared models for most domains, with exceptions in for beliefs about an incompetent clinician, a difficult client, and external barriers. This dissertation makes a valuable contribution by exploring culturally distinctive mental health beliefs and advocating for the benefits of mixed-methods approaches. It addresses the limitations of the contemporary psychological literature, which predominantly relies on theories, sampling, and methods prevalent in Western (i.e., “WEIRD”) contexts. These studies are proposed as an initial stride towards developing culturally grounded models for clinical assessment and care, catering to the needs of people from non-Western cultural backgrounds. The findings carry important implications for mental health research, policy, community care, practice, and education, especially in multicultural contexts.