The psychometric properties of a new high-level mobility outcome measure for Service Members (SMs) with traumatic lower limb loss called the Comprehensive High-level Activity Mobility Predictor (CHAMP) was developed in order objectively evaluate functional abilities and measure change in function throughout the rehabilitation process. The CHAMP was administered to a population of SMs with traumatic lower limb loss who were representative of those who have suffered limb loss in recent conflicts. In addition, a population of non-amputee Active Duty soldiers completed the CHAMP and provided normative data for high-level mobility and threshold levels of performance for those SMs with lower limb loss. A simple grading system, absent of floor and ceiling effects, generates a composite score providing a single numeric value representing the physical performance factors of high-level mobility in different plane of motion and under different conditions. The CHAMP was found to be a safe, reliable, valid, and responsive performance-based outcome measure of high-level mobility. It was found to have excellent interrater and test-retest reliability suggesting that it is a stable and repeatable measure of high-level mobility. Convergent construct validity and known group methods were utilized to establish the CHAMP as a valid measure of high-level mobility. Predictive models of CHAMP performance were established utilizing variables representing impairments of body structure and function and contextual factors by level of lower limb amputation. The CHAMP has the potential to be used for lower limb amputees throughout the rehabilitation process and could translate to the non-amputee population for assessment of high-level mobility capabilities.