This study investigated if an Acceptance and Commitment Therapy (ACT) intervention (ACT-Adjust) can facilitate psychological adjustment and reduce psychological distress following severe traumatic brain injury (TBI). The study design comprised a single centre, two-armed, Phase II pilot randomized controlled trial. Nineteen individuals with severe TBI (PTA ≥7 days) who met a clinical threshold for psychological distress (Depression Anxiety Stress Scales-21; DASS > 9) were randomly allocated to either ACT-Adjust (n = 10) or an active control, Befriending Therapy (n = 9), in conjunction with a holistic rehabilitation programme. Primary (psychological flexibility, rehabilitation participation) and secondary (depression, anxiety & stress) outcomes were measured at three-time points (pre, post and follow up). Significant decreases were found for DASS-depression (group by time interaction, F 1,17= 5.35, p =.03) and DASS-stress (group by time interaction, F 1,17= 5.69, p =.03) in comparison to the Befriending group, but not for the primary outcome measures. The reduction in stress post-treatment was classed as clinically significant, however interaction differences for stress and depression were not maintained at one month follow up. Preliminary investigations indicate potential for ACT in decreasing psychological distress for individuals with a severe TBI with further sessions required to maintain treatment gains. The pilot results suggest further investigation is warranted in a larger scale clinical trial.