Positive psychology research is increasingly being transferred to organizational contexts, and organizations are increasingly striving for healthier and more motivated employees. In this study, a three‐week self‐instructed online intervention which combines positive activities and mindfulness was developed and evaluated using a randomized‐controlled group design with employees. All exercises could be easily integrated into the daily working routine. The intervention is based on broaden‐and‐build theory, the two‐component model of mindfulness and the positive‐activity model. Results indicate that the intervention is effective in increasing work engagement, hope and sleep quality as well as in reducing fatigue. Practical implications for human resource departments and corporate health management are discussed. Practitioner points A three‐week mindfulness intervention can increase work engagement, hope, sleep quality, and reduce fatigue. Such activities can easily be integrated into the workday and thus, represent a realistic way for employees to improve motivation and reduce health impairment. ​