Background The growing concern of gestational diabetes is its impact on a mother and her child’s health. While a deficiency in vitamin D has been associated with glucose metabolism disturbances, strong evidence backing its preventive measures is still lacking. This study aimed to investigate if beginning oral vitamin D supplementation during the first trimester is capable of enhancing glucose metabolism and decreasing the incidence of gestational diabetes. Methods A randomized controlled trial was conducted at Khyber Teaching Hospital, Peshawar, from January 2022 to January 2023. One hundred and seven pregnant women in their first trimester were randomly divided into two groups: one received 2,000 IU of vitamin D daily, and the other received a placebo. Study participants were followed up to 28 weeks prenatal. Blood samples were analysed to assess fasting glucose, 2-hour OGTT, insulin, Hba1c, HOMA-IR, and serum vitamin D levels. GDM was diagnosed using IADPSG criteria. Results Participants in the vitamin D group exhibited significant enhancements in fasting glucose, Hba1c, and insulin resistance scores (p < 0.001) in comparison to other participants. GDM developed in 7.4% of the supplemented group participants versus 20.8% in the control group (p = 0.018). Conclusion It appears that gestational diabetes can be prevented with supplementation of Vitamin D in early pregnancy due to enhanced glucose metabolism. These results underscore the importance of including vitamin D testing and treatment in standard prenatal care.