Objective: To develop a systematic approach for magnetic resonance imaging (MRI) analysis, imaging spectrum, and classification system for the staging of post-COVID-19 head and neck mucormycosis. Method: The study included 63 post-COVID-19 patients with pathologically proven mucormycosis who underwent head and neck MR imaging. Three independent radiologists assessed the imaging spectrum of mucormycosis, MRI characteristics of sino-nasal mucormycosis, and extra-sinus extension, and submitted a final staging using a systematic approach and a proposed categorization system. A consensus reading was considered the reference imaging standard. The kappa statistics were used to assess the categorization system's diagnostic reliability. Results: The overall interreader agreement of the MR staging system was very good (k-score = 0.817). MR imaging spectrum involved localized sino-nasal mucormycosis (n = 7 patients, 11.1%), sino-nasal mucormycosis with maxillo-facial soft tissue extension (n = 28 patients, 44.5 %), sino-nasal mucormycosis with maxillo-facial bony extension (n = 7 patients, 11.1%), sino-naso-orbital mucormycosis (n = 13 patients, 20.6%), and sino-nasal mucormycosis with cranium or intracranial extension (n = 8 patients, 12.7%). Extra-sinus extension to the orbit and brain did not have significant association with involvement of the posterior ethmoid/sphenoid sinuses and maxillofacial regions (p > 0.05). MRI-based staging involved four stages: stage 1 (n = 7, 11.1%); stage 2 (n = 35, 55.6%), and stage 3 (n = 13, 20.6%), and stage 4 (n = 8, 12.7%). Involvement of the bone and MR-based staging were significant predictors of patients’ mortality p = 0.012 and 0.033, respectively. Conclusion: This study used a diagnostic-reliable staging method to define the imaging spectrum of post-COVID-19 head and neck mucormycosis and identify risk variables for extra-sinus extension.