Background: Research on youth positive mental health (PMH) lacks comprehensiveness. We reviewed literature to (i) identify and understand concepts related to youth PMH and (ii) to summarize their definitions under broad conceptual themes. Method: We conducted a systematic review using PRISMA methodology. The protocol was registered in PROSPERO database (ID:CRD42020203712). Pubmed, Embase, PsycINFO, and OpenGrey databases were searched for publications that examined, assessed, explained, or defined PMH concepts in youth populations. Methods included searching, independent screening and review using pre-determined inclusion and exclusion criteria, extraction, coding, and iterative thematic syntheses of literature. Results: Of 3427 unique records identified, 105 articles from 26 countries met review criteria. Qualitative analysis resulted in 22 broad themes of youth PMH. These included interpersonal relationships (interpersonal competence, school connectedness, etc.), positive emotions (feel and create pleasant emotions, gratitude, etc.), self-efficacy (strengths, human agency, etc.), life satisfaction (global assessment of one’s life), and personal growth (goal achievement, life aspirations, etc.). Five novel concepts related to youth PMH were identified. Conclusions: Our review summarized and operationalized multiple concepts of youth PMH for applications in research, evaluation, and public health improvement.