Introduction: Single-visit root canal treatment has gained significant attention as a promising approach for efficiently managing endodontic cases as it can reduce treatment time and increase patient comfort. However, its success in treating complex cases, especially molars, still needs to be evaluated. Single-visit root canal treatment is a non-surgical conservative treatment of teeth with irreversible pulp inflammation. This technique aims to do the full root canal procedure, including cleaning, shaping, and obturation in one sitting. Case Illustration: A female patient, 18 years old, complained of caries in her mandibular left first molar and felt pain when drinking cold water. Clinical examination showed caries on tooth #36, with normal response to vitality and percussion. The radiological examination revealed a normal periapical area. The diagnosis was asymptomatic irreversible pulpitis and treated with a single-visit root canal treatment. Four root canal preparations were performed using a rotary file, obturated with the single cone technique, followed by zirconia onlay restorations at the next visit. Conclusion: Single-visit root canal treatment of mandibular molars proved effective and efficient. Benefits in reduced treatment time, increased patient comfort, and comparable success rates with multi-visit treatments. The treatment performed in this case was clinically and radiologically successful.