Background/Objectives: Temporomandibular disorders affect the muscles used for chewing, the temporomandibular joint, and other related tissues, resulting in pain, limited mobility, and dysfunction of the masticatory muscles. Physical therapy plays a critical role in treatment. Manual therapy can trigger neurophysiological mechanisms that contribute to pain relief and a reduction in muscle activation. Evaluations of different manual therapy techniques are needed on this topic. The main objective of this study was to evaluate the effects of a specific manual therapy technique (the mandibular muscle energy technique) in adults with temporomandibular disorders. Methods: A randomized, parallel clinical trial was conducted, and 31 participants were recruited into an experimental group and 30 were recruited into a control group in order to analyze its effects on outcomes such as pain, pain threshold to pressure, mandibular mobility, and kinesiophobia. Pre- and post-intervention assessments were performed, followed by statistical analyses to verify the intra- and intergroup changes. Results: The results showed that the mandibular muscle energy technique produced positive effects with significant differences in the intra- and intergroup comparisons for pain threshold to pressure, mandibular mobility, and kinesiophobia, demonstrating its efficacy and safety as a treatment option for adults with temporomandibular disorders, with proven effects in the short term. Conclusions: The effects obtained and the absence of side effects showed that this technique can be integrated into multimodal treatment along with other types of interventions in patients with temporomandibular disorders.