Background: While combined diet and physical activity interventions are recommended, evidence specific to low-risk pregnant women remains limited. As responses to combined interventions may vary by pre-pregnancy BMI, maternal health status and pregnancy outcomes, targeted evaluation in low-risk pregnant women is needed. Inconsistencies across studies, along with the lack of a comprehensive synthesis of both effects and intervention components, further limit their implementation. Objective: Our aims were to assess the effects of combined diet and physical activity interventions on gestational weight gain among low-risk women and to systematically characterize the intervention components. Design: We conducted a systematic review and meta-analysis following the Cochrane Handbook guidelines and PRISMA 2020. Methods: Eight databases and trial registries were searched from inception to 16 March 2026. Two reviewers independently conducted study selection, data extraction and risk of bias assessment. Intervention components were coded using the TIDieR checklist. The quality of included studies was assessed using the updated Cochrane risk of bias 2.0 tool. Meta-analyses were performed using Review Manager 5.4, and certainty of evidence was assessed using the GRADEpro online tool. Results: A total of 10 studies involving 3977 pregnant women were included. Combined diet and physical activity interventions significantly reduced total gestational weight gain (GWG) (MD = −0.78 kg, 95% CI: −1.12 to −0.44, p < 0.00001) and the risk of excessive gestational weight gain (EGWG) (OR = 0.63, 95% CI: 0.49–0.81, p = 0.0003). Additionally, individually delivered physical activity components and those implemented in healthcare facilities appeared to be associated with lower total GWG (MD = −0.76 kg, 95% CI: −0.98 to −0.53, p < 0.00001). For EGWG, lower risk was observed in interventions using combined face-to-face and remote formats (OR = 0.54, 95% CI: 0.41–0.72, p < 0.0001) and moderate frequency (diet: OR = 0.64, 95% CI: 0.51–0.81, p = 0.0002, physical activity: OR = 0.65, 95% CI: 0.52–0.83, p = 0.0004). Conclusions: Combined diet and physical activity interventions were associated with reduced total GWG and lower EGWG risk in low-risk pregnant women. Intervention characteristics, such as individual delivery formats, combined face-to-face and remote formats, moderate frequency and implementation in healthcare facilities, may be related to intervention effectiveness. Registration number: CRD420251013116 (PROSPERO).