Pelvic actinomycosis is a rare, chronic infection caused by Actinomyces israelii that can mimic pelvic malignancy, particularly in women with prolonged intrauterine device (IUD) use. Diagnosis is challenging due to nonspecific clinical and radiological features. We present the case of a 49-year-old woman misdiagnosed with appendicitis and later found to have extensive pelvic actinomycosis involving the abdominal wall, bladder, uterus, and small bowel. Surgical resection with wide margins was followed by prolonged antibiotic therapy. Histopathology confirmed the diagnosis. The patient recovered completely over a 12-month follow-up. This case highlights the importance of considering actinomycosis in the differential diagnosis of pelvic masses and the role of comprehensive preoperative evaluation and multidisciplinary management.