Background The emergence of mucormycosis as a life-threatening fungal infection after the coronavirus disease of 2019 (COVID-19) is a major concern and challenge, but there is limited information on the risk factors for mortality in patients. Methods We conducted a prospective cohort study from May 2021 to April 2022 to determine the in-hospital outcomes of post-COVID-19 mucormycosis during the intensive care unit (ICU) stay. The sample of the study was collected as consecutive sampling using all accessible patients in the study period. The Statistical Package for Social Sciences (SPSS), version 25 (IBM, Chicago, Illinois, USA) was used for statistical analysis. Results Among 150 patients with post-COVID-19 mucormycosis, the majority had a primary sinus infection (86.0 %), while 11.3 % had both sinus and ocular infections, and 2.7 % had sinus and cutaneous infections. Around 21 % (n = 31) of patients deceased after staying in the ICU for a median (range) of 45.0 (10.0–145.0) days. The majority of the patients who deceased had pneumonia patches on computed tomography (CT) (90.3 %) while none of the patients who were discharged had pneumonia patches (p < 0.001). The deceased group had higher rates of pulmonary embolism (93.5 %) compared to the surviving groups (21.8 %). In a multivariate Cox regression analysis, the risk of death was higher in older patients above 60 years old (hazard ratio (95 %CI): 6.7 (1.73–15.81)), increase among patient with history of steroid administration (hazard ratio (95 %CI): 5.70 (1.23–10.91)), who had facial cutaneous infection with mucormycosis (hazard ratio (95 %CI): 8.76 (1.78–25.18)), patients with uncontrolled diabetes (hazard ratio (95 %CI): 10.76 (1.78, 65.18)), and total leukocytic count (TLC>10 ×103 mcL) (hazard ratio (95 %CI): 10.03 (3.29–30.61)). Conclusions Identifying high-risk patients especially old diabetic patients with corticosteroid administration and detecting their deterioration quickly is crucial in reducing post-COVID-19 mucormycosis mortality rates, and these factors must be considered when developing treatment and quarantine strategies.