Abstract The incidence rate of gestational diabetes mellitus (GDM) remains high among pregnant women in the second trimester of pregnancy. However, the main clinical approach to alleviate the symptoms of GDM is to control the diet. Our study explored the therapeutic effects of omega-3 fatty acids (ω-3 FAs) on GDM at the cellular and animal levels. We found that ω-3 FAs can promote the transformation of M0 macrophages into anti-inflammatory M2 macrophages. The transformed M2 macrophages promoted β-oxidation and reduced hepatocyte lipid synthesis (P < 0.05), thereby promoting hepatic function and preventing the excessive accumulation of lipid droplets in the hepatocyte cell line HepG2. Supplementation of ω-3 FAs in pregnant GDM mice significantly reduced fasting blood glucose levels, glucose tolerance test, and insulin tolerance test indices, and lipid accumulation in the liver and effectively prevented the occurrence of liver fibrosis (P < 0.05). These therapeutic effects may be mediated through the anti-inflammatory effects of ω-3 FAs (P < 0.05). ω-3 FAs also had positive effects on the offspring of pregnant GDM mice, as demonstrated by reduced birth mortality and improved glycemic stabilization (P < 0.05). In conclusion, this study provides a possible translational medicine strategy for the treatment of GDM.