Background: Sciatic nerve schwannomas are rare benign tumors that can develop along the nerve’s course, from the pelvis to the thigh. Giant schwannomas, defined as those exceeding 5 cm, are particularly rare and may alter the tumor’s anatomical relationship with the nerve, impacting surgical strategy. Methods: A PRISMA 2020-compliant systematic review was conducted using the terms (“sciatic” AND “schwannoma”) for publications from 2000 to October 2024. Of 166 identified articles, we excluded those lacking giant schwannoma cases or involving syndromic associations. We also report a novel case from our center. Results: Our patient, a 35-year-old woman, presented with tingling and discomfort while sitting, localized to the left thigh, without radicular pain or motor deficits. MRI revealed a 14 × 7 cm mass. This is, to our knowledge, the first reported case of a giant solitary sciatic schwannoma of these dimensions located exclusively in the thigh, resected via intracapsular dissection with nerve monitoring, that was fully documented and reported. The review yielded 22 relevant articles, most involving pelvic or pelvic–thigh junction locations, with low recurrence rates. Conclusions: Giant sciatic schwannomas may be asymptomatic and slow-growing. This case is notable for tumor’s location, large size, and successful nerve-sparing surgical outcome.