Aims Horner’s syndrome post tonsillectomy is a rare complication with only 17 documented cases in literature. This study aims to assess the association between tonsillectomy and Horner’s syndrome, identifying its incidence, mechanisms, outcomes and guide surgeons in refining techniques to enhance patient safety and postoperative care. Methodology This study combines a case report of a 7-year-old female who developed Horner’s syndrome post-tonsillectomy with a systematic review of 17 cases from 1933 to 2024. The databases PubMed, Medline, and Embase were searched using the terms “Horner’s syndrome” OR “oculosympathetic palsy” AND “tonsillectomy.” Articles meeting inclusion criteria were critically appraised, and data on patient demographics, surgical techniques, use of topical anaesthesia, and patient outcomes were analysed using and chi-square tests. Results The systematic review included 17 cases of Horner’s syndrome post-tonsillectomy, with ages ranging from 2 to 37 years and a predominance of females. Various surgical techniques, including cold steel dissection, radiofrequency ablation, and electrocautery, were used. The relationship between surgical technique and recovery was not statistically significant (p = 0.43). However, the use of topical anaesthesia showed a significant association with resolution rates (p = 0.012). Short-term outcomes varied, with 59% of cases showing persistence of symptoms for months to years, while some resolved within 24 hours. Conclusion Horner’s syndrome, though rare, is a potential complication of tonsillectomy. This study highlights the importance of understanding the possible mechanisms, the role of topical anaesthesia and surgical technique. The findings suggest that when local anaesthetic causes Horner’s syndrome, recovery is likely. Nonetheless, persistent symptoms in many cases underscore the need for careful surgical dissection and postoperative monitoring.