Neurological diseases affect more than 50 million people living with persistent upper limb impairments worldwide, and 40% of patients remain impaired even after intensive hospital care. Wearable robots have been developed for enhancing functionality in activities of daily living (ADL). The role of forearm movement is as crucial as the hand and wrist. However, the coincidence of the rotation axis with the forearm presents design challenges, and thus there are few studies on wearable devices for assisting forearm pronation/supination movement. In this study, we propose a bioinspired soft wearable skin-brace for the forearm pronation/supination to assist patients in ADL and perform rehabilitation training. The low-profile design that can fit the forearm like clothing combines features of a rail structure and tendon driving mechanism with high transfer efficiency. We conducted a biomechanical analysis to quantify the movement of wrist landmarks during forearm rotation, as well as a performance evaluation and user tests with our prototype. We demonstrate that it can provide patients with sufficient and compliant support in terms of range of motion and output torque. The user-friendly design allows patients to don and doff the device independently and quickly, as well as for individual customization. With the advantage of not restricting other joint movements, the device also shows the possibility of co-use with other rehabilitation devices.