Research has suggested that individuals with greater dispositional mindfulness (i.e., nonjudgmental, present-focused attention) are more likely to quit smoking, but the underlying mechanisms are unclear. This study investigated mechanisms linking mindfulness and early smoking abstinence using ecological momentary assessment (EMA). Participants were 355 smokers (33% Caucasian, 33% African American, 32% Latino; 55% female) receiving smoking cessation treatment. Mindfulness was assessed at baseline and on the quit date. For 4 days prequit and 1 week postquit, participants completed up to 4 EMAs per day indicating levels of negative affect (NA), positive affect (PA), smoking urges, and affect regulation expectancies. Mean, slope, and volatility were calculated for each prequit and postquit EMA variable. Associations among mindfulness, EMA parameters, and abstinence on the quit day and 7 days postquit, as well as indirect effects of mindfulness on abstinence through EMA parameters, were examined. Mindfulness predicted higher odds of abstinence in unadjusted but not covariate-adjusted models. Mindfulness predicted lower NA, higher PA, and lower affective volatility. Lower stress mediated the association between mindfulness and quit-day abstinence. Higher ratings of happy and relaxed, and lower ratings of bored, sad, and angry, mediated the association between mindfulness and postquit abstinence. Mindfulness appeared to weaken the association between craving and postquit abstinence. This study elucidates real-time, real-life mechanisms underlying dispositional mindfulness and smoking abstinence. During the early process of quitting smoking, more mindful individuals appeared to have more favorable emotional profiles, which predicted higher likelihood of achieving abstinence 1 week after the quit date. (PsycINFO Database Record (c) 2019 APA, all rights reserved).