Purpose: The aim of this study was to examine the cross-sectional and longitudinal associations of 24-h movement behaviors (sleep, sedentary behavior (SB), light physical activity (LPA), and moderate-to-vigorous physical activity (MVPA)) with body composition and cardiometabolic health in i) early and ii) late pregnancy (gestational weeks 14 and 37). Methods: This observational study utilized cross-sectional (n = 273) and longitudinal data (n = 242) from the HealthyMoms trial. Time spent in movement behaviors over seven consecutive 24-h periods (ActiGraph wGT3x-BT accelerometer), body composition (Bod Pod), and cardiometabolic health indicators (glucose levels, homeostatic model for insulin resistance (HOMA-IR), systolic and diastolic blood pressure, metabolic syndrome (MetS) score) were measured in early and late pregnancy. Results: In early pregnancy, reallocating time to MVPA from LPA, SB, and sleep was associated with lower MetS score (adjusted gamma = -0.343, P = 0.002). Correspondingly, reallocating time to LPA from SB and sleep in early pregnancy was associated with lower body weight (adjusted gamma = -5.959, P = 0.047) and HOMA-IR (adjusted gamma = -0.557, P = 0.031) at the same time point. Furthermore, reallocating time to LPA from SB and sleep in early pregnancy was associated with lower fat mass index (adjusted gamma = -0.668, P = 0.028), glucose levels (adjusted gamma = -0.315, P = 0.006), HOMA-IR (adjusted gamma = -0.779, P = 0.004), and MetS score (adjusted gamma = -0.470, P = 0.027) in late pregnancy. The changes in behaviors throughout pregnancy were not associated with body weight, body composition, and MetS score in late pregnancy. Conclusions: Our results demonstrated that increasing LPA or MVPA while reducing SB and sleep was associated with lower weight and more favorable cardiometabolic health in early pregnancy. In contrast, LPA in early pregnancy seems to be a stimulus of enough intensity to improve body composition and cardiometabolic health indicators in late pregnancy.