In recent years, both mindfulness and character strengths have started to garner interest in industrial and organizational psychology. The growing research interest in their effects on employee well-being and performance, individually, has strong practical implications for organizations. Given the interconnection of mindfulness and character strengths, the present study examined the effectiveness of training that combined the two practices regarding well-being and work-related outcomes, and it tested the potential mediators of the effects at work. A total of 63 participants from various job branches were randomly assigned to three conditions: (a) mindfulness-based strengths practice (MBSP), (b) mindfulness-based stress reduction (MBSR), and (c) wait-list control. Participants' applicability of character strengths at work, well-being, perceived stress, job satisfaction, and task performance (supervisor rating) were assessed before and after the intervention, and 1, 3, and 6 months afterward. A set of linear mixed-effects models was applied, modeling changes in participants' outcome variables over time. Potential mediators for the intervention effect of MBSP at work were tested using four criteria adapted from a previous study. Results showed the MBSR was effective for increasing well-being, reducing perceived stress, and increasing job satisfaction, whereas the MBSP was effective for increasing well-being, job satisfaction, and task performance. These findings suggest that mindfulness alone seems to function better when regarding well-being at work, while fusing character strengths on top of it seems to influence the participants, on a motivational level, and thus bolsters task performance. (PsycINFO Database Record (c) 2019 APA, all rights reserved).