SummaryThis study assessed associations of actigraphy‐assessed sleep with adiposity and serum cardiometabolic outcomes in emerging adults, and whether sex and race modified these associations. Data on 147 emerging adults (age = 19.4 ± 1.3 years; body mass index = 26.4 ± 7.0 kg m⁻²; 59% female; 65% White) from RIGHT Track Health were used. Actigraphy‐based sleep measures included sleep duration, sleep efficiency, sleep timing midpoint, day‐to‐day sleep duration and sleep timing midpoint variability. Combined sleep duration and sleep timing behaviours were also derived (early‐bed/late‐rise, early‐bed/early‐rise, late‐bed/late‐rise, late‐bed/early‐rise). Outcomes included body mass index and BodPod‐assessed fat mass index, fasting serum leptin, C‐reactive protein, and homeostatic model assessment‐insulin resistance. Sleep duration was 5.4 h per night. We noted an inverse association between sleep duration and homeostatic model assessment‐insulin resistance. The early‐bed/early‐rise group had greater body mass index, C‐reactive protein and homeostatic model assessment‐insulin resistance compared with the early‐bed/late‐rise group (referent). Sex modified associations of sleep efficiency with C‐reactive protein; stratified results revealed positive association between sleep efficiency and C‐reactive protein in males, but not females. Race modified associations of sleep duration with body mass index and leptin, and of sleep duration variability with C‐reactive protein. Stratified analyses revealed inverse associations between sleep duration with body mass index and leptin in Black, multiracial/other race individuals only. Positive association between sleep duration variability and C‐reactive protein was noted in White individuals only. Shorter sleep duration, particularly when combined with earlier sleep timing, is associated with greater adiposity and serum cardiometabolic outcomes. Additional studies are needed to assess individual‐ and contextual‐level factors that may contribute to sex and race differences in sleep health and cardiometabolic risk in emerging adults.