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Primary colonic lymphoma is a rare neoplasm. Perforation with fecal peritonitis as the initial manifestation is an exceptional and life-threatening complication requiring emergency surgical management. We report a case of diffuse large B-cell lymphoma of the colon presenting with fecal peritonitis, highlighting the diagnostic challenges and multidisciplinary approach required. A 70-year-old female patient with a history of hypertension presented to the emergency department with an acute abdomen, septic shock, and generalized peritonitis. Abdominal computed tomography (CT) revealed fecal peritonitis secondary to perforation of a cecal tumor. Emergency right oncologic colectomy with double stoma was performed because of generalized purulent peritoneal contamination. Histopathological and immunohistochemical examination confirmed diffuse large B-cell lymphoma, germinal center type, with a high proliferation index (antigen Ki-67, 90%), cluster of differentiation 79a (CD79a)-positive, and cluster of differentiation 3 (CD3)-negative. The postoperative course was uneventful after a two-day intensive care unit (ICU) stay. The patient received four cycles of immunochemotherapy based on rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP). At six months, PET-CT evaluation demonstrated a partial response, and treatment is ongoing to complete six cycles. This case illustrates that colonic lymphoma should be considered in the differential diagnosis of acute abdomen with tumor perforation. Emergency colectomy serves both diagnostic and therapeutic purposes by controlling the septic source and providing tissue for definitive histological diagnosis. Multidisciplinary management combining emergency surgery and adjuvant immunochemotherapy is essential for optimizing outcomes in this rare presentation.