Women with overweight or obesity (OWOB) have an increased risk of cesarean birth, preterm birth (PTB), and high birth weight infants. Although regular exercise decreases this risk in healthy weight women, these associations have not been explored in OWOB. Women were randomized at 13–16 weeks’ gestation to 150-min of moderate-intensity exercise (n = 131) or non-exercising control (n = 61). Delivery mode, gestational age (GA), and birth weight (BW) were obtained via electronic health records. Pregnant exercisers had no differences in risk of cesarean birth, PTB, or BW compared to control participants. OWOB exercisers had higher rates of cesarean birth (27.1% vs. 11.1%), trends of higher PTB (15.3% vs. 5.6%), but normal weight babies relative to normal weight exercisers. Controlling for race and body mass index (BMI), maternal exercise reduced the relative risk (RR) for cesarean birth from 1.63 to 1.43. Cesarean births predicted by pre-pregnancy BMI and fitness level, whereas BW was predicted by race, gestational weight gain (GWG), pre-pregnancy fitness level, and exercise level. Cesarean birth was predicted by pre-pregnancy BMI and fitness level, while maternal exercise reduced the magnitudes of the relative risks of cesarean birth. Maternal exercise, pre-pregnancy fitness level, and GWG predict neonatal BW.