In this case report, primary pulmonary mycobacteriosis in a domestic cat was assessed using histopathological and immunohistochemical methods. The cat was admitted to a private veterinary clinic and presented with hyporexia, lethargy, and dyspnea with an abdominal component. For diagnostic purposes, thorax radiography was performed. Radiographic lung imaging showed the presence of opaque foci that were widely distributed throughout the lung. The cat’s condition gradually deteriorated, and the cat died 2 hours after being brought to the clinic. Following owner consent, gross post-mortem examination was performed immediately after death at the same clinic. White foci measuring 2–10 mm in diameter covered the surface of the lungs and were present throughout the parenchyma, mostly multifocally and occasionally coalescing. No other macroscopical pathological findings were observed in other organs or on the skin. Some of the lung tissue with macroscopic lesions underwent further histopathological and immunohistochemical examination. Multifocal to coalescing areas of caseous necrosis (without a fibrous capsule) with, karyorrhectic nuclei, and numerous macrophages were observed. Ziehl-Neelsen staining revealed many acid-fast bacteria. Immunohistochemical staining revealed positive immunostaining for Mycobacterium spp. This case study highlights the importance of considering zoonotic risks in cats diagnosed with primary pulmonary mycobacteriosis.