Background: Essential tremor (ET) is characterized by action tremor of the arms, which can interfere substantially with daily activities. Pharmacotherapy may be ineffective or associated with side effects, and stereotactic surgery is invasive. Hence, new accessible treatment options are urgently needed. An easy-to-use and lightweight orthotic device that exerts joint damping may provide an alternative solution for reducing tremor in daily activities. Objective: Our goal was to assess the efficacy of a novel anti-tremor orthosis (STIL) in reducing clinical and accelerometry measures of distal arm tremor in ET. Methods: In a randomized crossover single-blinded trial in 24 ET patients in a hospital setting, we compared three conditions: no orthosis (baseline), a sham device, and the anti-tremor orthosis (order randomized). The orthosis, but not the sham device, passively damped joints in the forearm. Participants performed seven tasks from the Tremor Research Group Essential Tremor Rating Scale (TETRAS). The two co-primary outcome measures were: clinical tremor severity (video-scored TETRAS) and tremor power (accelerometry). Patient satisfaction was self-assessed using the Dutch Quebec User Evaluation of Satisfaction with assistive Technology. Conditions were compared using Wilcoxon signed-rank tests. Results: The anti-tremor orthosis significantly reduced TETRAS scores compared to sham and baseline (baseline: 19.0 ± 3.2, sham: 13.7 ± 3.9, orthosis: 9.9 ± 3.6; mean ± standard deviation). Similar effects were observed for tremor power, which was reduced by 87.4% (orthosis vs. baseline) and 59.5% (orthosis vs. sham) across all tasks. A total of 71% of participants were (very) satisfied and 12.5% reported minor adverse events (discomfort/redness of skin). Conclusion: The anti-tremor orthosis had a clinically relevant tremor-reducing effect in ET in a controlled setting, offering potential for a new treatment to manage ET in daily activities.