Introduction: Participation rates and quality-of-life (QoL) have been a major focus of rehabilitation programmes and outcome studies following traumatic brain injury (TBI). The extent to which mobility limitations impact on participation rates and QoL has not been thoroughly explored. The main aim of this study was to investigate the relationship between mobility limitations, participation rates and QoL following TBI. Methods: Thirty-nine people who had sustained an extremely severe TBI were recruited from a major rehabilitation facility. Mobility was quantified using the high-level mobility assessment tool (HiMAT). The Brain Injury Community Rehabilitation Outcome (BICRO-39) and Community Integration Questionnaire (CIQ) were used to measure participation rates and the shorter version of the World Health Organization Quality of Life (WHOQoL-BREF) and Assessment of Quality-of-Life (AQoL-2) were used to measure QoL. Results: Mobility was most strongly correlated with the total BICRO-39 score (r = −0.60, p < 0.001) and the mobility domain (r = −0.59, p < 0.001) of the BICRO-39. Although mobility had a significant relationship with health-related QoL, AQoL-2 (r = 0.60, p < 0.001), it was most strongly related to the AQoL-2 independent living domain (r = 0.79, p < 0.001). Conclusion: Greater capacity to mobilize was associated with higher participation rates and better QoL.