Despite the well-documented health benefits of physical activity in older adults, participation levels remain low. With rapid global population ageing, intensive efforts are needed to encourage higher levels of participation to ameliorate the negative effects of physical inactivity for older individuals and society as a whole. The aim of this qualitative study was to inform future physical activity promotion interventions by examining factors contributing to low activity levels among older people undertaking less than half the recommended level of moderate-to-vigorous physical activity (MVPA). Semi-structured interviews were conducted with 102 (65% female) community-dwelling Western Australians aged 60+ years (mean = 71.52, standard deviation = 6.26) who engaged in ⩽75 minutes of MVPA per week as measured by accelerometers. Several modifiable and unmodifiable barriers were identified, of which poor health featured most prominently. Lifetime physical inactivity, caring duties, low motivation, misperceptions of physical activity and ageing, and a lack of affordable and attractive options were the other barriers identified. The results suggest that strategies are needed to raise awareness of current physical activity guidelines, normalise engagement in MVPA throughout the lifespan, develop initiatives to motivate participation, improve the availability of affordable physical activity programmes that are attractive to this population segment, and facilitate participation among those with intensive caring responsibilities.