In two studies, we examined primary appraisal as a potential mechanism of workplace mindfulness, grounded in the Transactional Model of Stress and Coping. In Study 1, multilevel structural equation modeling utilizing diary data from 58 employees across 5 working days showed that daily challenge appraisal mediated the positive relationship between mindfulness and high-activation positive affect, and daily threat appraisal mediated the negative relationship between mindfulness and high-activation negative affect. In Study 2, 69 employees participated in a randomized control trial comparing self-directed mindfulness training with a wait-list control. Latent growth curve modeling demonstrated that the intervention produced a greater increase in daily mindfulness relative to the control condition. In turn, the rate of change in daily mindfulness influenced the change rate of appraisal, and daily appraisal influenced affect, as expected. Together, these studies indicate one way in which mindfulness may help employees to thrive at work is by adaptively shaping the stressor appraisal process, and that connecting mindfulness training to primary appraisal may bolster the potential beneficial effects in the work context. (PsycInfo Database Record (c) 2022 APA, all rights reserved).