Although several randomized clinical trials have tested the effect of prenatal dietary supplements on plasma glucose and lipid levels in non-pharmacologically managed gestational diabetes mellitus patients (GDM), a rigorous meta-analytic compendium lacks in the context. Therefore, this study aims to address this evidence gap. Eligible trials retrieved from searches in the PubMed, Embase, and Scopus databases were appraised using the Revised Cochrane risk-of-bias tool for randomized trials (RoB 2). The weighted mean differences (WMD) between dietary supplements and placebo were estimated using random-effect meta-analysis models for plasma glycemic and lipid markers. Meta-regression analysis ensued for effect modifier identification. The statistical significance estimation happened at p < 0.05 (95% confidence interval). This review included 19 trials (mostly Iranian and of low risk of bias primarily) of > 8000 GDM patients. Meta-analysis showed favorable effects of dietary supplementation on fasting plasma glucose (WMD: -5.42 mg/dL, p < 0.001), homeostasis model assessment indexes- insulin resistance (HOMA-IR; WMD: -1.02, p < 0.001), quantitative insulin sensitivity check index (WMD: 0.01, p < 0.001), total cholesterol (TC; WMD: -7.70 mg/dL, p = 0.006), triglycerides (WMD: -10.23 mg/dL, p = 0.0083), TC/high-density lipoprotein (WMD: -0.31 mg/dL, p < 0.001), low-density lipoprotein (WMD: -5.79 mg/dL; p < 0.001) and very-low-density lipoprotein (WMD: -5.67 mg/dL, p < 0.001) levels. However, the HOMA- ß-cell function didn't increase (WMD: -17.91, p < 0.001). Baseline maternal age (ß = 0.28, p = 0.014) and GDM diagnostic criteria (ß = 0.90, p = 0.012) were effect moderators of HOMA-IR and body mass index (BMI) (ß = 6.07, p = 0.022) and supplement type (solo versus combined) (ß = 14.99, p = 0.006) were effect moderators of triglyceride levels. Altogether, antenatal dietary supplements achieved control over plasma glycemic and lipid profiles in non-pharmacologically treated GDM patients. Maternal age and GDM diagnostic criteria moderated HOMA-IR levels. BMI and supplement-type moderated triglyceride levels. The online version contains supplementary material available at 10.1007/s40200-023-01369-0.