Background/Objectives: Synchronous ipsilateral supraclavicular lymph node metastases (sISLMs) in breast cancer are rare and associated with poor prognosis. The optimal locoregional treatment strategy remains unclear, particularly regarding the role of supraclavicular lymph node dissection (SLND). Methods: We conducted a systematic review and network meta-analysis, including studies published up to end December 2023, to compare the outcomes of SLND combined with radiotherapy (RT) and systemic therapy (ST), SLND with ST alone, and ST alone, using RT + ST as the reference. Results: Ten studies involving 3346 patients were included for overall survival (OS) analysis, and six studies were included for disease-free survival (DFS). SLND + RT + ST showed similar OS and DFS compared to RT + ST. Sensitivity analyses revealed that SLND limited to level V improved OS (HR: 0.47, 95% CI: 0.29–0.77), while more extensive dissections (level V+) worsened outcomes (HR: 1.41, 95% CI: 1.10–1.80). Conclusions: These findings suggest that selective SLND may benefit certain patients, but broader application should be approached with caution pending results from future randomized trials.