The Canadian 24-Hour Movement Guidelines for Children and Youth (≥60 minutes of moderate-to-vigorous physical activity per day, ≤2 hours of recreational screen time per day, and 9-11 hours of sleep per night for 5-13 years old) are associated with better physical health, but less is known about how these behaviors are related to mental health. This study examined the association of meeting these guideline recommendations with internalizing and externalizing behaviors among youth. A large and broadly representative cross-sectional sample of 9- to 11-year-old U.S. youth (N = 11,875) from the Adolescent Brain and Cognitive Development study was analyzed. Internalizing and externalizing behaviors were measured using the Child Behaviour Checklist. Associations were examined using negative binomial regression adjusted for several confounders. Compared to meeting none of the recommendations, meeting recommendations for screen time and sleep but not physical activity was associated with a lower prevalence ratio of total, internalizing, and externalizing behaviors. Meeting two or all three recommendations was more strongly associated with these outcomes than meeting one recommendation or none. The prevalence ratio of the group meeting all three recommendations was .77 (95% confidence interval [CI]: .68-.86) for total problem scores, .78 (95% CI: .68-.89) for internalizing problem scores, and .79 (95% CI: .68-.91) for externalizing problem scores. Meeting the 24-hour movement guidelines was associated with a lower risk of internalizing and externalizing behaviors in youth. These associations were mainly explained by meeting the screen time and sleep duration recommendations.