Background <p>Traumatic brain injury (TBI) is a leading cause of disability worldwide. Rehabilitation in the intensive care unit (ICU) is a recommended intervention for the critically ill. However, the safety and effectiveness of physical rehabilitation in adults admitted to the ICU with TBI is currently unknown.</p> Objectives <p>The primary objective was to evaluate the safety of physical ICU rehabilitation in adults with TBI, and secondary outcomes aimed to evaluate its effect upon physical outcomes and length of admission.</p> Methods <p>Five electronic databases were searched up to 1 September, 2025, including studies investigating physical ICU rehabilitation interventions in adults with acute TBI. A narrative synthesis of safety outcomes was conducted owing to heterogeneity. Meta-analysis was performed for secondary outcomes using the random-effects model to compare pooled data for rehabilitation and no-rehabilitation groups. Risk of bias was assessed using the ROBINS-E tool for observational studies and the RoB2 tool for randomised studies.</p> Results <p>Overall, 13 studies consisting of 3582 adults with TBI were included. Four studies reported safety outcomes, reporting no or low rates of adverse events. Meta-analysis identified an increase in the Perme ICU Mobility Scores at ICU discharge in those that received ICU rehabilitation [Mean Difference 3.25 (2.05–4.44), <i>p</i> &lt; 0.00001]. Risk of bias assessment identified very high risk of bias in observational studies and some concerns of bias in randomised studies.</p> Conclusions <p>Physical rehabilitation for adults with TBI in the ICU is potentially safe with suggested benefit upon mobility status at ICU discharge. Further high-quality studies of ICU rehabilitation for adults with TBI are required.</p> <p><i>Trial Registration</i>: PROSPERO CRD420251131380.</p>