BACKGROUND: Dog ownership has been suggested to encourage physical activity in older adults and may enhance resilience to poor environmental conditions. This study investigates the role of dog ownership and walking as a means of supporting the maintenance of physical activity in older adults during periods of inclement weather. METHODS: The analysis used data from the European Prospective Investigation into Cancer and Nutrition Norfolk cohort. Daily physical activity (counts per minute) and minutes of sedentary behaviour were measured using accelerometers over 7 days. Three types of environmental conditions, day length, precipitation and maximum temperature, were date matched with daily physical activity. A multilevel first-order autoregressive time-series model quantified the moderating effect of self-reported dog ownership and walking on the association between physical activity and weather factors. RESULTS: Among the 3123 participants, 18% reported having a dog in their households and two-thirds of dog owners walked their dogs at least once a day. Regular dog walkers were more active and less sedentary on days with the poorest conditions than non-dog owners were on the days with the best conditions. In days with the worst conditions, those who walked their dogs had 20% higher activity levels than non-dog owners and spent 30 min/day less sedentary. CONCLUSION: Those who walked dogs were consistently more physically active than those who did not regardless of environmental conditions. These large differences suggest that dog walking, where appropriate, can be a component of interventions to support physical activity in older adults.