Abstract Background Many community-dwelling older adults experience limitations in (instrumental) activities of daily living, resulting in the need for homecare services. Whereas services should ideally aim at maintaining independence, homecare staff often take over activities, thereby undermining older adults’ self-care skills and jeopardizing their ability to continue living at home. Reablement is an innovative care approach aimed at optimizing independence. The reablement training program ‘Stay Active at Home’ for homecare staff was designed to support the implementation of reablement in the delivery of homecare services. This study evaluated the implementation, mechanisms of impact and context of the program. Methods We conducted a process evaluation alongside a 12-month cluster randomized controlled trial, using an embedded mixed-methods design. One hundred fifty-four homecare staff members (23 nurses, 34 nurse assistants, 8 nurse aides and 89 domestic workers) from five working areas received the program. Data on the implementation (reach, dose, fidelity, adaptations and acceptability), possible mechanisms of impact (homecare staff's knowledge, attitude, skills and support) and context were collected using logbooks, registration forms, checklists, log data and focus group interviews with homecare staff (n = 23) and program trainers (n = 4). Results The program was largely implemented as intended. Homecare staff's average compliance to the program meetings was 73.4%; staff members accepted the program, and particularly valued its practical elements and team approach. They experienced positive changes in their knowledge, attitude and skills about reablement, and perceived social and organizational support from colleagues and team managers to implement reablement. However, the extent to which homecare staff implemented reablement in practice, varied. Perceived facilitators included digital care plans, the organization’s lump sum funding and newly referred clients. Perceived barriers included resistance to change from clients or their social network, complex care situations, time pressure and staff shortages. Conclusions The program was feasible to implement in the Dutch homecare setting, and was perceived as useful in daily practice. Nevertheless, integrating reablement into homecare staff's working practices remained challenging due to various personal and contextual factors. Future implementation of the program may benefit from minor program adaptations and a more stimulating work environment. Trial registration ClinicalTrials.gov (Identifier NCT03293303). Registered 26 September 2017.