There is growing interest in the possibility of harnessing positive emotional experiences associated with acting sustainably in order to reinforce pro-environmental behaviors. However, most research to date has been based on cross-sectional data or hypothetical scenarios. We conducted a pre-registered longitudinal intervention study relating positive emotions (feeling happy, satisfied, and good) to real-life clothing-related behaviors (repair, acquisition, and disposal). We also measured boredom and frustration, as they may reduce sustainable clothing-related behaviors. 62 participants attended a hands-on clothing repair workshop; 51 others in a control group did not. Across both groups, individuals who anticipated more positive emotions from repairing clothes reported higher repair intentions after the intervention period and four weeks later. In the workshop group, anticipated positive emotions also predicted more repair behaviors four weeks later. In addition, people who experienced more positive emotions from participating in the workshop reported higher repair intentions immediately afterwards and four weeks later. Regarding negative emotions, anticipated boredom reduced repair intentions over time in both groups, and experienced boredom was associated with fewer repairs four weeks later in the workshop group. No significant effects were observed for frustration. Overall, repair intentions increased over time, but several behavioral outcomes did not change (e.g., clothing acquisition). This finding emphasizes the need to measure real-life behaviors rather than only intentions. These data demonstrate that positive emotions are associated with sustainable clothing behaviors over time. Such skilled-based group interventions could potentially help combat the negative impact of the fast fashion industry on climate change.