PURPOSE: To perform the process evaluation of an intervention that aims to facilitate clinical healthcare professionals (HCP) to provide Maastricht Work-Related Support (WRS) to working patients with a chronic disease. METHODS: A mixed-methods approach was applied to address reach, efficacy, adoption, implementation, and maintenance (RE-AIM framework) as well as context of the Maastricht WRS intervention. Qualitative data included interviews with HCPs (N = 10), patients at two time points (N = 10 and N = 9), and field notes. Quantitative data included screening logbooks of HCPs, patient screening forms, and a questionnaire for patients. Content analysis or computation of frequencies was applied where applicable. RESULTS: Twenty-eight HCPs participated in the intervention (reach). They had a low attitude toward providing Maastricht WRS themselves (adoption). During clinical consultations, they addressed work for 770 of 1,624 (47%) persons of working age. Only 57% (437/770) had paid work, of which 10% (44/437) acknowledged a current need for support. Discussing work during clinical consultations by HCPs was hindered by other medical priorities and patients not disclosing problems (implementation). Over time, Maastricht WRS was less consistently provided (maintenance). Patients reported a positive impact of the intervention, such as fitness for work (efficacy). Context (e.g., lack of urgency, priority, time, and management support) played a pivotal role in the implementation. CONCLUSION: This evaluation showed that HCPs had a positive attitude toward WRS in general, but their attitude toward provide Maastricht WRS themselves in daily clinical care was low. Recommendations include improving HCPs' attitude, addressing WRS as a key policy point, and facilitating time.