Background: Childhood is a critical period for brain development, and the behaviours that comprise a typical 24-hour day contribute to cognitive performance in children. This study investigated the relationship between cognition and meeting the 24-hour movement behaviour guidelines of ≥60 minutes of physical activity, ≤2 hours of recreational screen time, and 9-11 hours of sleep per day in 9-10 year olds. Methods: This study presents cross-sectional data from the first annual curated release of the Adolescent Brain Cognitive Development Study (ABCD) - a 10-year longitudinal, observational study investigating brain development in American children. Data were collected from 21 study sites across the United States between September 2016 and 2017. Participants were 4,524 American children aged 9-10 years. Exposures were physical activity, recreational screen time, and sleep duration. The primary outcome was global cognition and secondary outcomes were crystallized and fluid intelligence. Findings: The mean (SD) number of guideline recommendations met was 1·1 (0·9). Overall, 50·9% of participants met the sleep recommendation, 36·5% met screen time, and 17·5% met the physical activity recommendation. 65·3% of participants met at least 1, whereas 4·7% of participants met all 3 recommendations. Multi-level regression analysis revealed a significant positive gradient between global cognition and each additional recommendation met [β=1·48 (95% CI: 0·86, 2·11), p<0·001]. For combinations of behaviours, there was a significant positive association between global cognition and meeting sleep screen [β=5·26 (95% CI: 3·67, 6·86), p<0·001] or meeting the screen-only [β=4·37 (95% CI: 2·61, 6·13, p<0·001] compared to not meeting any recommendations.