Background: Vitamin D deficiency is associated with cardiovascular dysregulation and increased blood pressure; however, evidence in pregnant women in South Asia remains limited. This study aimed to evaluate the correlation and regression between maternal serum vitamin D levels and blood pressure components during late pregnancy. Methods: A hospital-based case–control study was conducted at Sir Salimullah Medical College Mitford Hospital, Dhaka, from March 2019 to March 2020, involving 106 pregnant women (53 preeclamptic and 53 normotensive). Serum 25-hydroxyvitamin D [25(OH)D] levels were measured using a chemiluminescence immunoassay and categorized as deficient (≤20 ng/mL), insufficient (21–29 ng/mL), or sufficient (≥30 ng/mL). Blood pressure was recorded according to standard protocols. Correlation and linear regression analyses were performed using SPSS version 23.0, with significance set at p < 0.05. Results: Serum vitamin D levels were inversely correlated with both systolic (r = –0.449, p < 0.001) and diastolic (r = –0.449, p < 0.001) blood pressures. Regression analysis indicated that each 1 ng/mL rise in serum vitamin D corresponded to a decrease of 1.68 and 1.2 mmHg in systolic and diastolic pressure, respectively. Sun exposure duration and antenatal attendance were positively associated with vitamin D sufficiency. Conclusion: Maternal serum vitamin D concentration was inversely associated with systolic and diastolic blood pressures. Maintaining adequate vitamin D levels through sunlight exposure and supplementation may support cardiovascular stability during pregnancy.