We present an 84-year-old female patient with a very rare form of primary non-urothelial squamous cell carcinoma of the bladder, found incidentally during emergency exploratory laparotomy for a perforated pre-pyloric gastric ulcer. The bladder tumor was positive for CK5/6, CK903, and thrombomodulin biomarkers, as well as for high-risk HPV (16, 18, and 31). Based on a literature review of non-urothelial bladder cancers, specifically non-bilharzial squamous cell carcinoma, we believe our patient had a very rare form of primary non-urothelial squamous cell carcinoma of the bladder. The presence of these tumor markers and the lack of clinical evidence to suggest another primary origin, such as anus, rectum, cervix, or uterus, support this conclusion. This case provides an interesting example of a very rare incidental finding during an emergent procedure.