For individuals with spinal cord injury (SCI) who walk with conventional knee–ankle–foot orthoses (KAFOs), locked knees and compensatory trunk and upper-limb motions can limit gait efficiency. This study presents a lightweight active KAFO that provides powered knee assistance while still being used like a conventional KAFO. The device integrates a backdrivable knee actuator within a two-level control architecture: a high-level controller, comprising a finite state machine and a parametric trajectory generator that computes the knee reference from user-selected step height and speed, and a low-level position-based impedance controller tracks this trajectory. Step height and speed can be adjusted in real time via an on-board touchscreen interface, and a ramp-based timing strategy allows smooth changes in gait cycle duration over roughly a two-fold range. A pilot case study was conducted on a single adult with chronic incomplete SCI who walks with KAFOs and a walker. Two configurations were compared: his usual conventional KAFO set-up and one with the proposed active KAFO. Clinical outcome measures included the 10m walking test (10MWT), the 6 min walking test (6MWT) and end-of-test heart rate. With the active KAFO, the participant achieved a higher 10MWT walking speed than with his conventional KAFOs, whereas no clear difference was observed in 6MWT distance and heart rate responses remained in a similar range. These preliminary results suggest that an active KAFO with an adjustable knee trajectory and on-board tuning of gait parameters may offer a feasible intermediate option between conventional KAFOs and full lower-limb exoskeletons.