Purpose <p>Poor sleep is a long-term sequela of cancer and its treatment. Moderate-to-vigorous physical activity (MVPA) is associated with improved health outcomes among cancer survivors and has been suggested as a nonpharmacological method to improving sleep. We evaluated the efficacy of a MVPA intervention to improve sleep among cancer survivors.</p> Methods <p>We conducted a randomized controlled trial among 415 cancer survivors embedded within the Cancer Prevention Study-3 cohort. Survivors were randomized to a year-long, web-based MVPA program. MVPA was assessed via hip-worn actigraphy at baseline, 3&#xa0;months, 6&#xa0;months, and 1&#xa0;year. We evaluated sleep through the SATED sleep health questionnaire, PROMIS Sleep Disturbance Scale, and device-measured duration and efficiency. An intent-to-treat (ITT) analysis was performed, and secondary analyses were conducted based on measured MVPA levels with generalized additive mixed-effects models.</p> Results <p>Survivors reported similar sleep health and patterns to the general US population. We observed no significant changes to sleep between treatment groups in ITT models. Though not statistically significant, there appeared to be heterogeneity based on baseline sleep disturbance (moderate-to-severe sleep disturbance: <i>β</i>_SATED = 0.73 (95% CI − 0.09, 1.60) vs mild-to-normal sleep disturbance: <i>β</i>_SATED = − 0.26 (95% CI − 0.57, 0.05)). Participants that engaged in more MVPA at the end of the trial reported better sleep health (<i>p</i>-value = 0.04) and less sleep disturbances (<i>p</i>-value = 0.11).</p> Conclusions <p>The MVPA intervention was more effective at improving sleep among survivors with sleep disturbances at baseline. Increasing MVPA improved sleep among cancer survivors</p> Implications for Cancer Survivors <p>Increasing MVPA among cancer survivors with sleep disturbances may be a viable strategy for improving sleep.</p>