Newly emerged severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of the ongoing coronavirus disease 2019 (COVID-19) pandemic, which has caused extensive mortality and morbidity and wreaked havoc on socioeconomic structures . The urgent need to better understand SARS-CoV-2 biology and enable continued development of effective countermeasures is aided by the production of laboratory tools that facilitate SARS-CoV-2 research . We previously created a directly accessible SARS-CoV-2 toolkit containing user-friendly reverse genetic (RG) infectious clones of SARS-CoV-2 . Here, using K18-human ACE2 (hACE2) mice, we confirmed the validity of RG-rescued SARS-CoV-2 viruses to reproduce the infection profile, clinical disease, and pathogenesis already established in mice infected with natural SARS-CoV-2 isolates, often patient derived . RG-rescued SARS-CoV-2-infected K18-hACE2 mice developed substantial clinical disease and weight loss by day 6 postinfection . RG-rescued SARS-CoV-2 was recovered from the lungs and brains of infected K18-hACE2 mice, and infection resulted in viral pneumonia with considerable changes in lung pathology, as seen previously with natural SARS-CoV-2 infection . In mice infected with RG-rescued SARS-CoV-2-mCherry, mCherry was detected in areas of lung consolidation and colocalized with clinically relevant SARS-CoV-2-assocated immunopathology . RG-rescued SARS-CoV-2 viruses successfully recapitulated many of the features of severe COVID-19 associated with the K18-hACE2 model of SARS-CoV-2 infection . With utility in vivo, the RG-rescued SARS-CoV-2 viruses will be valuable resources to advance numerous areas of SARS-CoV-2 basic research and COVID-19 vaccine development.IMPORTANCE To develop COVID-19 countermeasures, powerful research tools are essential . We produced a SARS-COV-2 reverse genetic (RG) infectious clone toolkit that will benefit a variety of investigations . In this study, we further prove the toolkit's value by demonstrating the in vivo utility of RG-rescued SARS-CoV-2 isolates . RG-rescued SARS-CoV-2 isolates reproduce disease signs and pathology characteristic of the K18-hACE2 mouse model of severe COVID-19 in infected mice . Having been validated as a model of severe COVID-19 previously using only natural SARS-CoV-2 isolated from patients, this is the first investigation of RG-rescued SARS-CoV-2 viruses in K18-hACE2 mice . The RG-rescued SARS-CoV-2 viruses will facilitate basic understanding of SARS-CoV-2 and the preclinical development of COVID-19 therapeutics.