Traumatic brachial plexus injury (TBPI) is a serious neurological condition most often resulting from trauma. This condition is among the most debilitating injuries affecting the upper limb. The injury is typically categorized as preganglionic or postganglionic based on the site of trauma, proximal to or distal to the dorsal root ganglion (DRG). TBPI results in movement deficits of the upper limb with impaired muscle strength and sensitivity. This case report details the extensive rehabilitation of a 27-year-old male patient who was involved in a road traffic accident, resulting in injuries to the left upper extremity characterized by a loss of motor function and sensation. Additionally, the incident caused injuries to the left lower extremity, leading to a mid-shaft femur fracture and fractures of the metatarsals. The patient received a comprehensive clinical evaluation, along with diagnostic tests and imaging studies, which resulted in a confirmed diagnosis of pre- and post-ganglionic injury to the left upper extremity, as well as polytrauma affecting the left lower extremity. Tailored rehabilitation strategies were employed to address the diverse symptoms, including multi-sensory strategies, sensory re-education, and graded motor imagery rehabilitation. Progressive improvement of the range of motion, strength, and endurance in the lower extremities, along with the enhancement of neuromuscular control, is essential. This rehabilitation program can be used as a reference for establishing early treatment strategies.