Purpose: Low levels of physical activity during pregnancy go along with increased risks for numerous health complications. We investigated whether an integrated lifestyle intervention leads to higher levels of physical activity and reduces the rate of excessive gestational weight gain (EGWG). Methods: We conducted a randomized-controlled trial on 97 pregnant women, randomly assigned to receive an additional telehealth lifestyle intervention (experimental group, EG; n = 49) or conventional antenatal care (control group, CG; n = 48). The core lifestyle intervention comprised regular video calls, providing integrated personal support and motivation to physical activity. The primary outcome was change in physical activity measured in steps per day. An additional exploratory outcome was the proportion of participants with EGWG. Results: The mean step count during the third trimester was 6483 steps/day (EG) and 5957 steps/day (CG), respectively (p = 0.078). Repeated-measures ANOVA revealed a significant interaction effect (p = 0.045) reflecting an overall increase of 497 steps per day in the EG vs. a decrease of 300 steps per day in the CG. The proportion of participants who met the IOM recommendation for total weight gain during pregnancy was significantly higher in the EG (p = 0.048) and the ratio of women that gained excessively was higher in the CG (p = 0.026). Conclusions: We assume that the personalized online intervention supports women in increasing or at least maintaining their level of physical activity during the course of pregnancy. Additionally, it reduces the rate of excessive weight gain.