Abstract Background A main goal during the return to work (RTW) process after a long-term sickness absence due to common mental disorders (CMDs), is to restore and maintain an employees’ work ability to enable sustained work participation. To date, surprisingly little research has examined the concept of work ability during the RTW process with CMDs. To better understand how to restore employees’ work ability during RTW with CMDs, both quantitative and qualitative research is needed. The goal of this mixed methods study is to expand the understanding of restoring work ability during the RTW process with CMDs. Methods In this mixed methods follow-up study of N = 286 participants, work ability was quantitatively assessed with the Work Ability Score (WAS, range 0-10) at five measurement points (0, 6, 12, 18 and 30 months) during 30 months of follow-up. In a sub-sample, the qualitative work ability experiences of N = 32 participants were jointly analysed with their quantitative work ability ratings at 6 and 12 months. Results In the joint analysis, three groups of qualitative work ability experiences together with their respective quantitative work ability ratings emerged: Employees with (1) poor work ability (WAS 0-3), who did not RTW yet and described great difficulties in coping with everyday life; (2) moderate work ability (WAS 4-6), who mainly did RTW, but still showed a certain level of fragility; and (3) good to very good work ability (WAS 7-10), who mainly returned within 12 months and reported many individual and work accommodations to restore and maintain their work ability. Conclusions The joint evaluation of work ability ratings and experiences allowed a deeper understanding of restoring work ability during the RTW process. This knowledge may help occupational health professionals and other key RTW stakeholders to provide more tailored support during the RTW process and to promote a sustainable RTW for employees with CMDs. Key messages • Restoring and maintaining the work ability of employees with common mental disorders during the return to work process is crucial for their sustained work participation. • Achieving a good to very good work ability helps returning employees with common mental disorders to ‘stay and thrive’ at work again.