Background: Neonatal hyperbilirubinemia is a frequent clinical condition in the early neonatal period and remains a major cause of hospital readmission. While most cases are physiological, prolonged or severe jaundice may indicate underlying systemic disorders, including congenital hypothyroidism, which affects bilirubin metabolism through delayed hepatic maturation. Objective: Toevaluate the relationship between neonatal serum total bilirubin levels and thyroid function parameters, specifically thyroid-stimulatinghormone (TSH) and free thyroxine (FT4), in full-term neonates with hyperbilirubinemia. Methodology: This observationalstudy was conducted in the Department of Pediatrics, Dhaka Shishu (Children) Hospital and Institute (DSH&I). A total of 120 full-term neonates with clinical features of hyperbilirubinemia were enrolled. Serum total bilirubin was measured using the Grot–Jendrassik method, while FT4 and TSH levels were assessed by chemiluminescence immunoassay. Data were analyzed using SPSS version 25. Pearson’s correlation coefficient was used to assess the relationship between bilirubin and thyroid hormone levels, with p < 0.05 considered statistically significant. Results: The mean serum bilirubin level was 11.21 ± 3.08 mg/dL, mean TSH was 3.38 ± 3.57 µIU/mL, and mean FT4 was 1.27 ± 1.11 ng/dL. Serum bilirubin showed a significant positive correlation with TSH (r = 0.626, p < 0.001) and a significant negative correlation with FT4 (r = −0.594, p < 0.001). Conclusion: The study demonstrates a significant association between thyroid dysfunction and neonatal hyperbilirubinemia, highlighting the importance of thyroid function evaluation in jaundiced neonates for early diagnosis and management.