Objectives: Maintaining physical activity for older residents in care homes maximises their physical and mental health and wellbeing, independence, dignity and quality of life. Unfortunately, most residents do not participate in regular physical activity. Active Residents in Care Homes, ARCH, was designed to increase physical activity by facilitating whole-system change in a care home. We evaluated whether ARCH can be delivered, its effects on resident's physical activity, wellbeing and costs. Design: Feasibility study. Setting: Three residential care homes. Participants: Care home residents and staff. Intervention: Occupational and physiotherapists implemented ARCH over 4 months with an 8month follow-up. Main outcome measures: Assessment of Physical Activity, Pool Activity Level, EQ5D-5L, Dementia Care Mapping, cost of implementing ARCH, health and social care utilisation. Results: After implementing ARCH, residents displayed more positive behaviours, better mood and engagement and higher physical activity levels, but these improvements were not sustained at 8-month follow-up. The cost (2016 prices) of implementing ARCH was £61,037, which equates to £1,650/resident. Healthcare utilisation was £295/resident (SD320) in the 4 months prior to ARCH, £308/resident (SD406) during the 4-month implementation and £676/resident (SD438) in the 8month follow-up. Conclusions: The ARCH programme can be delivered, it may have some short-term benefits and is affordable. Rather than have unrealistic increases in the health and longevity of older care home residents, ARCH may slow the decline in physical, mental and emotional well-being usually seen in older people in care homes, return some dignity and improve their quality of life in their last months or years.