To assist patients with lower limb dysfunction in mobility, standing, and walking, this paper proposes a novel device that integrates the functions of lower limb exoskeleton, wheelchair, and sit-to-stand (STS) transfer assistance. We designed a 10-degree-of-freedom lower limb exoskeleton based on gait analysis. To satisfy human–machine compatibility, the hip joint was conceptualized as a remote center-of-motion (RCM) mechanism, the knee joint was developed as a cam mechanism, and the ankle joint was designed as a revolute pair. We constructed a kinematic model of the exoskeleton by adopting the product-of-exponential (POE) formula. The STS transfer assistance mechanism was designed based on Stephenson III six-bar linkage through path synthesis methods. The length of this six-bar mechanism was determined based on using Newton–Jacobi iterative techniques. We connected the STS assistive mechanism to the wheelchair frame, and then, we connected the exoskeleton to the STS transfer assistive mechanism. The experimental results demonstrated that the STS assistance path aligned closely with human buttock trajectories, and the walking assistance paths corresponded with natural human gaits. This device produces a new choice for patients with lower limb dysfunction.