Background. We examined whether physical activity in early adulthood, late midlife, and old age as well as cumulative physical activity history are associated with changes in physical functioning and mortality in old age. Methods. Data are from participants aged 65 years or older enrolled in the InCHIANTI study who were followed up from 1998–2000 to 2007–2008 (n = 1,149). At baseline, participants recalled their physical activity levels at ages 20–40, 40–60, and in the previous year, and they were categorized as physically inactive, moderately active, and physically active. Physical performance was assessed with the Short Physical Performance Battery and self-reported mobility disability was evaluated at the 3-, 6- and 9-year follow-up. Mortality follow-up was assessed until the end of 2010. Results. Physical inactivity at baseline was associated with greater decline in Short Physical Performance Battery score (mean 9-year change: −2.72, 95% CI: −3.08, −2.35 vs −0.98, 95% −1.57, −0.39) and greater rate of incident mobility disability (hazard ratio 4.66, 95% CI 1.14–19.07) and mortality (hazard ratio 2.18, 95% CI 1.01–4.70) compared to physically active participants at baseline. Being physically active throughout adulthood was associated with smaller decline in physical performance as well as with lower risk of incident mobility disability and premature death compared with those who had been less active during their adult life. Conclusions. Higher cumulative physical activity over the life course was associated with less decline in physical performance and reduced rate of incident mobility disability and mortality in older ages.