This study examined changes in PA participation and determinants in older adults throughout the COVID-19 pandemic. 110 older adults (76 females and 34 males [73±5 years]) completed validated questionnaires to measure demographic characteristics and PA participation over 7 days. A sub-sample of 59 participants completed semi-structured interviews. Inductive thematic analysis was used to explore changes to PA during COVID-19. Extent of self-isolation, garden ownership, cohabitation status and external practical support did not significantly affect PA volume. Poor psychological wellbeing and lack of resources and/or knowledge contributed to 53% of participants reporting a decrease in PA throughout lockdown. Participation in walking and gardening PA had increased, and technology-based fitness resources facilitated PA, including in those who previously performed no deliberate PA. Overall findings indicate that home-based resources and education surrounding PA may help older adults become more active during social isolation, whether regularly or during a pandemic.