Background/Objectives: Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection. Sepsis is a significant cause of hospital admission and the leading reason for admission to the ICU and is associated with high mortality. Vitamin D has shown promising immunomodulatory effects by upregulating the antimicrobial peptide, cathelicidin. However, previous studies analysing the use of calcitriol in sepsis have shown variable results and did not utilise APACHE II (Acute Physiology and Chronic Health Evaluation II) scores as endpoints. This study evaluates the efficacy of intramuscular calcitriol in patients admitted to the ICU with sepsis, focusing on its impact on APACHE II scores. The primary aim was to determine if intramuscular calcitriol improved APACHE II scores from day 1 to day 7 or discharge from the ICU, whichever was earlier. Secondary outcomes included 28-day mortality, ventilator days, vasopressor days, ICU stay length, adverse events, and hospital-acquired infections in ICU patients. Methods: This was a triple-blinded phase III randomised control trial. A total of 152 patients with suspected sepsis were block-randomised to receive either intramuscular calcitriol (300,000 IU) (n = 76) or a placebo (n = 76). The trial was registered with the Clinical Trials Registry-India (CTRI No: CTRI 2019/01/17066) following ethics committee approval and was not funded. Results: There was no significant difference in APACHE II scores between the calcitriol and placebo groups from day 1 to day 7 (p = 0.382). There were no significant changes in 28-day mortality (14.4% vs. 17%, p = 0.65), number of days on a ventilator (5 vs. 5, p = 0.84), number of days on vasopressors (3 vs. 3, p = 0.98), length of ICU stay (10 days vs. 11 days, p = 0.78), adverse events (27.6% vs. 19.7%, p = 0.25), and hospital-acquired infections (17.1% vs. 15.8%, p = 0.82). Conclusions: There was no effect of intramuscular calcitriol in patients admitted to the ICU with sepsis.