Background: Insufficient physical activity (PA) is a risk factor for several noncommunicable chronic diseases. The World Health Organization stresses the need for national PA trend data to help inform strategies to arrest noncommunicable chronic disease incidence. The Active Australia Survey questionnaire quantifies leisure-time physical activity. Despite being used repeatedly in large population surveys, these data have never been analyzed as a single dataset. This study established temporal trends for aerobic PA sufficiency prevalences in the Australian adult (18–75+ y) population, 2002–2012, based on leisure-time physical activity. Methods: Individuals’ records from 58 surveys were merged into a master database (N = 443,211) and categorized according to sufficiency of PA (150 minutes of PA per week). Data were age/sex standardized to the 2011 Australian population. PA sufficiency trends were determined for the whole sample and sociodemographic subgroups. Results:Sufficient PA prevalences 2002–2012 increased from 55.9% (95% CI, 55.893–55.897) to 61.2% (95% CI, 61.223–61.267). No reported PA prevalences decreased from 16.1% (95% CI, 16.095–16.101) to 13.8% (95% CI, 13.745–13.811). This pattern persisted across most sociodemographic subgroups. Disparities between age groups, male/female, metropolitan/rural, and advantaged/disadvantaged categories, although present, were not diverging further. Conclusions: Levels of adult leisure-time physical activity are slowly increasing, but a substantial proportion of the population is still at increased risk of adverse health outcomes due to insufficient PA.