Although regular physical activity is recommended for pregnant women, compared to pre-pregnancy, antenatal physical activity often reduces or ceases completely. Drawing from the theory of planned behavior, self-determination theory, and theory on self-control, we aimed to test an integrative model of physical activity in a sample of pregnant women. The current study was conducted in Brisbane, Australia, in 2014–2015 using a prospective-correlational design with a one-week follow-up. Participants (N = 207, Time 1; Meanage = 30.03 years, SDage = 4.49 years) completed an initial survey measuring: intrinsic motivation from the self-determination theory, social cognitive constructs from the theory of planned behavior, and self-control from the self-control theory, followed by a self-report measure of physical activity one-week later (n = 117, Time 2). A well-fitting structural equation model accounted for 73 and 42 percent of the variance in intention and physical activity behavior, respectively. Perceived behavioral control and attitude, but not subjective norm, mediated the effect of intrinsic motivation on intention. Intention, perceived behavioral control, and self-control were positively associated with physical activity behavior. Future behavioral interventions aiming to promote physical activity during pregnancy, a period when the physical activity levels typically decline, should consider the multiple processes advocated in the integrative model as necessary for motivated action.