Background Sleeve gastrectomy (SG) continues to be one of the most popular bariatric procedures all over the world. Thyroid-stimulating hormone (TSH) frequently shows a slight elevation in patients with obesity. The effect of SG on thyroid hormones has been rarely investigated. Aim of the Study This study aimed to assess the short-term effect of SG on thyroid functions in Egyptian patients with morbid obesity and the potential predictors of the postoperative thyroid functions. Patients and Methods This study included patients undergoing SG at kasr al ainy hospitals. The patients underwent preoperative 3-, 6-, and 12-month postoperative analyses of the thyroid functions and other biochemical markers. Results The study included 106 patients who showed significant improvement in thyroid functions at the follow-up assessment. Twelve-month TSH positively correlated with the 12-month measures of LDL and HbA1c. TSH change at 12-month follow-up (TSH) was inversely correlated to 12-month BMI and positively correlated to preoperative TSH and 12-month percentage of total weight loss (TWL%). Univariable linear regression analysis demonstrated that preoperative TSH (p < 0.001), 12-month TWL% (p = 0.042), 12-month HbA1c (p = 0.001), and 12-month LDL (p = 0.049) were significant predictors for the 12-month TSH levels. Multivariable analysis showed that only preoperative TSH levels (p < 0.001) and 12-month HbA1c levels (p = 0.021) could affect the 12-month TSH levels. Conclusion The current study supports the evidence of thyroid function improvement after sleeve gastrectomy. This improvement was affected by the amount of weight loss after surgery.