Abstract Introduction Hyperbaric oxygen therapy (HBOT) is a novel technique recently under investigation with intention to improve outcomes in traumatic brain injury (TBI). It increases the partial pressure of oxygen in the blood and tissues by inhaling pure oxygen in an environment pressurized to at least 1.4 times normal atmospheric pressure (ATM) at sea level. The rationale behind the use of HBOT in TBI is its potential to mitigate the secondary brain injury cascade initiated by the primary mechanical trauma. Tissue damage and neuroinflammation secondary to intricate and complex cellular biochemical processes are expected to be counteracted by increased oxygen availability during HBOT, which reduces oxidative stress and improves neuroplasticity. Materials and Methods All patients, except whose legal guardians denied informed consent, with moderate TBI presenting to the neurotrauma center, All India Institute of Medical Sciences, Rishikesh, Uttarakhand, India, were included within the study period of June 2022 to July 2023. Patient allocation was randomized into two arms: namely, treatment and control arm. Simple randomization was done using randomization mobile app, RRApp. Each patient received standard of care per the Brain Trauma Foundation guidelines. Patients randomized under the treatment arm additionally received adjuvant HBOT sessions. One session daily for 10 consecutive days. Session duration was for 60 minutes each at 1.4 ATM. The primary objective of the study was to compare the Glasgow Coma Score (GCS) at discharge and 3-month post-TBI Glasgow Outcome Scale-Extended (GOS-E) among patients in the treatment arm (those who received adjuvant HBOT) with those in the control arm (those who received only standard of care). Results The mean GCS (±standard deviation [SD]) at discharge in the treatment arm was 14.37 (±00.51) with a median of 14 and a range of 14 to 15. Comparatively, the mean GCS (±SD) at discharge in the control arm was 13.40 (±00.84) with a median of 13 and a range of 12 to 15. The difference between the two arms was statistically significant (p < 0.001). GOS-E at 3 months postinjury for the treatment arm was 7.62 ± 00.51 (mean ± SD) with a median of 8 (range: 7–8). For the control arm, GOS-E at 3 months postinjury was 6.40 ± 1.50 (mean ± SD) with a median of 7 (range: 4–8). The difference between the two arms was statistically significant (p < 0.001). Conclusion The current study concludes that early adjuvant HBOT using 1.4 ATM with one session of one-hour daily for 10 days among adults sustaining moderate TBI significantly improves GCS at 10 days. Early adjuvant HBOT is also associated with significantly improved GOS-E at 3 months postinjury compared to standard of care alone.