Cardiovascular diseases (CVDs) are a leading global health concern. Emerging evidence suggests a potential protective role of well-being in reducing CVD risk. We conducted a cohort analysis using the UK Biobank data set, encompassing 121 317 participants. We assessed the well-being of participants using a well-being index derived from baseline questionnaires. Well-being categories were derived by latent class analysis using general happiness and satisfaction with family, friendships, health, and finance situations. The relationship between well-being and 4 major CVDs was analyzed using Cox proportional hazards models and Mendelian randomization. The study also examined the impacts of well-being on lifestyle factors and inflammatory markers, and its mediating role in the well-being-CVD relationship. Higher well-being was associated with a significantly reduced risk of various CVDs. Latent class analysis identified 4 distinct well-being groups (low, variable, moderate-to-high, and high satisfaction), with higher satisfaction levels generally associated with lower risk of CVDs. Mendelian randomization suggested potential causal relationships between well-being and reduced risk of CVDs. Participants with greater well-being demonstrated healthier behaviors and lower levels of inflammatory markers. Mediation analysis indicated that lifestyle and inflammatory markers partially mediated the relationship between well-being and CVDs. This study demonstrates a robust inverse association between well-being and the risks of CVDs, suggesting that enhancing well-being may be a viable strategy for CVD prevention. The role of lifestyle factors and inflammation as a mediator provides insight into possible biological pathways linking psychological states and cardiovascular health.