Autism spectrum disorder (ASD) is a persistent neurodevelopmental disorder frequently co-occurring with attention-deficit/hyperactivity disorder (ADHD) and behavior-related disorders. While behavioral therapy is the first-line option to manage the core symptoms of ASD, pharmacological therapy is sometimes needed to treat acute problems, such as agitation and aggressive behaviors. Recent guidelines recommend the use of neuroleptics to reduce psychomotor agitation in patients with ASD. However, as children with ASD are often drug-resistant, alternative treatments are often justified. Reports from the literature have indicated that intravenous valproate (IV-VPA) can be effective in reducing agitation in psychiatric patients, with a lower frequency of adverse events compared to conventional treatments. However, as the related findings are occasionally inconsistent, IV-VPA is not yet an approved option in the context of clinical psychiatry. We aim to improve knowledge of the IV-VPA treatment option for emergency psychiatric treatment in pediatric patients. We report the case of an 11-year-old boy suffering from a complex neurodevelopmental condition who experienced a psychotic episode with severe aggressive and disruptive behaviors and was successfully treated with IV-VPA. Furthermore, we provide an updated literature review on this topic. In our case, first-line therapies proved to be ineffective. To the contrary, IV-VPA led to safe and prompt clinical success, which is in line with other reports. Based on our literature review, IV-VPA can be highly effective and reduces the risk of adverse events that frequently occur with the use of high-dose standard medications in emergency psychiatry.