<p>Cancers of the oral cavity (OCC) and oropharynx (OPC) affect nearly 59,000 individuals annually in the United States. [¹⁸F]-fluorodeoxyglucose Positron Emission Tomography/Magnetic Resonance Imaging ([¹⁸F]FDG-PET/MRI) is an advanced hybrid modality integrating metabolic and anatomical imaging and is increasingly being studied for evaluating these malignancies. This review examines its clinical utility in diagnosis, staging, and management of OCC and OPC. Current evidence suggests that [¹⁸F]FDG-PET/MRI may improve diagnostic and prognostic accuracy by providing superior soft tissue contrast and complementary metabolic information, particularly for detecting perineural spread and muscle involvement. For tumor staging, it may offer improved tumor delineation compared with contrast-enhanced MRI, especially in the presence of dental artifacts. Detection of nodal metastases may also be enhanced compared to MRI alone through combined assessment of morphological features and maximum standardized uptake value (SUVmax). Emerging data indicate that [¹⁸F]FDG-PET/MRI may aid detection of distant metastases and prediction of human papillomavirus status through apparent diffusion coefficient (ADC) correlations. Associations between imaging biomarkers such as SUV and ADC and histopathological markers including Ki-67 and Programmed Death-Ligand-1 support its role in assessing tumor aggressiveness. Additionally, [¹⁸F]FDG-PET/MRI can assist in biopsy planning and may reduce unnecessary neck dissections. Compared to PET/CT, [¹⁸F]FDG-PET/MRI offers superior soft tissue contrast, lower radiation, fewer dental artifacts, and improved detection of intracranial metastases. Overall, it is a promising tool for improving diagnosis, staging, and treatment planning, although further studies are needed to define its precise role in routine practice.</p>