While high levels of activity and exercise training have been associated with improvements in sleep quality, minimum levels of activity likely to improve sleep outcomes have not been explored. A two-armed parallel randomized controlled trial (N=41; 30 females) was designed to assess whether increasing physical activity to the level recommended in public health guidelines can improve sleep quality among inactive adults meeting research diagnostic criteria for insomnia. The intervention consisted of a monitored program of â¥150Â min of moderate- to vigorous-intensity physical activity per week, for 6Â months. The principal end-point was the Insomnia Severity Index at 6Â months post-baseline. Secondary outcomes included measures of mood, fatigue and daytime sleepiness. Activity and light exposure were monitored throughout the trial using accelerometry and actigraphy. At 6Â months post-baseline, the physical activity group showed significantly reduced insomnia symptom severity (F8,26 Â =Â 5.16, PÂ =Â 0.03), with an average reduction of four points on the Insomnia Severity Index; and significantly reduced depression and anxiety scores (F6,28 Â =Â 5.61, PÂ =Â 0.02; and F6,28 Â =Â 4.41, PÂ =Â 0.05, respectively). All of the changes were independent of daily light exposure. Daytime fatigue showed no significant effect of the intervention (F8,26 Â =Â 1.84, PÂ =Â 0.18). Adherence and retention were high. Internationally recommended minimum levels of physical activity improve daytime and night-time symptoms of chronic insomnia independent of daily light exposure levels.