In response to rising mental health challenges and declining retention rates among college students, FlourishU was developed as a semester-long, credit-bearing first-year seminar designed to promote student well-being, academic success, and retention through the application of positive psychology. The seminar was developed in response to increasing mental health challenges and high dropout rates among college students. FlourishU offers a preventative, strengths-based approach to the first-year experience. The course is organized into four thematic units: positive identity, positive mind, positive doing, and positive connection. Each unit integrates evidence-based interventions aimed at fostering self-efficacy, a growth mindset, gratitude, optimism, resilience, grit, a sense of mattering, and connection. The curriculum is designed to be developmentally appropriate, inclusive, and impactful across diverse student populations. The paper outlines the theoretical foundation, course structure, implementation recommendations, and evaluation strategies for FlourishU, making the case for its adoption as a scalable, preventative intervention in higher education.