Using signature strengths at work has been shown to influence workers’ optimal functioning and well-being. However, little is known about the processes through which signature strengths lead to positive outcomes. The present research thus aimed at exploring the role of having a harmonious passion in the relation between using signature strengths and well-being. For this purpose, an intervention was developed where participants (n = 186) completed three activities aiming at developing their knowledge and use of their signature strengths at work. The results showed (1) that the intervention successfully increased participants’ use of their signature strengths, (2) that participants from the experimental group reported a higher use of their signature strengths at the end of the study than participants from the control group, and (3) that increases in the use of signature strengths reported by participants from the experimental group were related to increases in harmonious passion, which in turn led to higher levels of well-being.