Serratia marcescens represents an unusual yet potentially deadly cause of lower limb necrotizing fasciitis (NF). Compounding the already high mortality of NF, S. marcescens infections are usually associated with worse outcomes (i.e., amputation). Here we present the case of a 56-year-old immunocompromised man due to lupus nephritis who developed lower limb NF secondary to S. marcescens followed by nosocomial coronavirus disease 2019 (COVID-19) pneumonitis. Successful limb salvage was achieved through a multidisciplinary team approach from various specialties including plastic surgery, orthopedic surgery, anesthesiology, intensive care, respiratory medicine, and nephrology. At 11 months' follow-up, the patient was largely independent with activities of daily living and was able to ambulate. Unfortunately, he suffered a myocardial infarction at 19 months post-operatively and passed away. A review of the literature revealed only a handful of cases of lower limb NF due to S. marcescens and none with subsequent COVID-19. Therefore, this is the first report of such a case which should help with the clinical management of such cases going forward, especially with COVID-19 now becoming endemic in our communities and contributing to delayed presentations and increased mortality in NF.