The mindful reappraisal hypothesis of the Mindfulness-to-Meaning Theory (Garland et al. in Psychol Inquiry 26(4):293-314, 2015a; Psychol Inquiry 26(4):377-387, 2015b) proposes that mindfulness generates eudaimonic well-being by promoting positive reappraisal, the positive psychological process through which stressful events are re-construed as benign, meaningful, or growth-promoting. To test this hypothesis, we examined prospective relations between state mindfulness and positive reappraisal in a community sample participating in a mindfulness-based intervention (MBI). At seven weekly time points throughout the MBI, participants (N = 234) engaged in a 10-min mindfulness meditation exercise at home and completed a measure of the degree of state mindfulness experienced during the meditation, as well as a measure of their use of positive reappraisal over the previous week. Support for the mindful reappraisal hypothesis of the Mindfulness-to-Meaning Theory was found: in latent growth curve and multivariate autoregressive latent trajectory models, increases in the trajectory of state mindfulness experienced during meditation were significantly and robustly associated with more frequent use of positive reappraisal over the course of participation in the 8 week-long MBI. Thus, mindfulness and reappraisal may reciprocally enhance one another as interdependent components of a positive feedback loop whose structure might be best described as an upward spiral.