Background As the number of people living with dementia rapidly increases worldwide, the support provided by their informal caregivers remains key to the sustainability of most healthcare systems, this voluntary contribution representing 40% of the costs of dementia worldwide. Informal caregiving in dementia, however, is linked to long periods of chronic stress with frequent and serious negative consequences on the health and quality of life of the caregiver. A psycho-educative group intervention focusing on coping with the daily stress of dementia caregiving (“Learning to feel better… to help better”), developed in French-speaking Canada and showing broad effects on quality of life, was selected with the aim of 1) adapting it to a new cultural context (French-speaking Switzerland) based on identified facilitators and barriers, using a participative approach; and 2) conducting a feasibility study to evaluate whether the adapted programme showed similar or improved feasibility and effects compared to the original Canadian programme. Methods A mixed-methods concurrent nested design was used to evaluate the feasibility and the effects on five quantitative core outcomes. Additional qualitative data helped document in depth the acceptability and impact of the intervention. Results We shortened the programme from 30 to 21 hours in total, which resulted in increased accessibility, in terms of facilitated recruitment of participants and inclusion of a broader range of informal caregivers. There were significant reductions in subjective burden (effect size: d=-0.32) and psychological distress (d=-0.48), as well as decreases in the stress reactions of informal caregivers related to the behaviour problems of the persons with dementia (d=-0.57). The qualitative results emphasized the usefulness of providing informal caregivers with structured procedures for efficiently tackling everyday challenges, and of enabling learning through a variety of channels and activities. Conclusions Substantial improvements are associated with this 21-hour group intervention, organised in 7 sessions of 3 hours each, focused on learning more efficient strategies to cope with the daily stress of dementia caregiving. This intervention empowered informal caregivers to master their daily challenges with more confidence, satisfaction and calm. Trial registration: ISRCTN13512408 (registration date 17.05.2021, retrospectively registered).