Background Minor head trauma (MHT) is a common reason for emergency department (ED) admissions. Although the Canadian CT head rule (CCHR) provides criteria to guide brain imaging decisions, overuse of cranial CT remains a concern due to radiation exposure and healthcare costs. Optic nerve sheath diameter (ONSD), measured by ultrasonography, has emerged as a promising noninvasive marker of increased intracranial pressure. Objective This study aimed to evaluate the diagnostic performance of ultrasonographic ONSD measurement for detecting intracranial pathology in patients with MHT and to determine whether ONSD provides additional diagnostic value when used in conjunction with the CCHR. Methods This prospective observational study included 123 patients presenting to the ED with MHT. All participants underwent cranial CT imaging and bedside ultrasonographic measurement of ONSD. Intracranial pathology detected on CT was recorded. Receiver operating characteristic (ROC) analysis was performed to evaluate the diagnostic performance of ONSD measurements and the CCHR in predicting intracranial pathology. Results A total of 123 patients were included in the study, and intracranial pathology was detected on cranial CT in 31 patients (25.2%). Both right and left ONSD measurements were significantly higher in patients with CT pathology than in those without pathology (p < 0.001). ROC analysis demonstrated comparable diagnostic performance between ONSD measurements and the CCHR. Right ONSD showed the highest diagnostic accuracy (Area under the curve (AUC) = 0.756), followed by the CCHR (AUC = 0.751) and left ONSD (AUC = 0.732). Increased ONSD values were also associated with intensive care unit admission (p < 0.001). Conclusion Ultrasonographic ONSD measurement demonstrated a significant association with intracranial pathology and clinical outcomes in patients with MHT. ONSD showed diagnostic performance comparable to that of the CCHR and may serve as a rapid non-invasive adjunct to clinical assessment in the ED.