Objective <p>Mindfulness has gained increasing attention for its potential role in promoting health behaviors. However, previous studies have predominantly used variable-centered approaches and have lacked examination from a daily dynamic process perspective. This study examined the relationship between trait mindfulness and physical activity among young adults by integrating cross-sectional and diary designs.</p> Methods <p>Study 1 employed a large-sample cross-sectional design, analyzing data from 1,446 young adults through correlation analysis and latent profile analysis (LPA). Study 2 utilized a daily diary design, involving 206 young adults in an 11-day daily diary study, with data analyzed using hierarchical linear modeling.</p> Results <p>Study 1 demonstrated a positive association between trait mindfulness and physical activity. LPA revealed distinct mindfulness profiles, with the high mindfulness group reporting higher levels of physical activity. Study 2 not only confirmed the positive predictive role of trait mindfulness on daily physical activity levels but also revealed that individuals engaged in more physical activity on days when their mindfulness levels were higher.</p> Conclusions <p>These multi-method findings provided robust evidence that trait mindfulness was positively associated with physical activity. The findings supported mindfulness as a key factor in promoting healthy behaviors and offered empirical evidence for the future development of mindfulness-based personalized physical activity interventions.</p> <p>Preregistration: This study is not pre-registered.</p>