Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the etiological agent of the ongoing pandemic of 2019 CoV disease (COVID-19), which is already responsible for far more deaths than were reported during the previous public health emergencies of international concern provoked by two related pathogenic coronaviruses (CoVs) from 2002 and 2012. The identification of any clinically approved drug that could be repurposed to combat COVID-19 would allow the rapid implementation of potentially life-saving procedures to complement social distancing and isolation protocols. The major protease (Mpro) of SARS-CoV-2 is considered a promising target for drug interventions, based on results from related CoVs with lopinavir (LPV) an HIV protease inhibitor, that that can inhibit the Mpro of 2002 SARS-CoV. However, limited evidence exists for other clinically approved anti-retroviral protease inhibitors that may bind more efficiently to Mpro from SARS-CoV-2 and block its replication. Of high interest is atazanavir (ATV) due to its documented bioavailability within the respiratory tract, which motivated our evaluation on its ability to impair SARS-CoV-2 replication through a series of in vitro experiments. A molecular dynamic analysis showed that ATV could dock in the active site of SARS-CoV-2 Mpro with greater strength than LPV and occupied the substrate cleft on the active side of the protease throughout the entire molecular dynamic analysis. In a cell-free protease assay, ATV was determined to block Mpro activity at a concentration of 10 μM. Next, a series of assays with in vitro models of virus infection/replications were performed using three cell types, Vero cells, a human pulmonary epithelial cell line and primary human monocytes, which confirmed that ATV could inhibit SARS-CoV-2 replication, alone or in combination with ritonavir (RTV). In addition, the virus-induced levels of IL-6 and TNF-α were reduced in the presence of these drugs, which performed better than chloroquine, a compound recognized for its anti-viral and anti-inflammatory activities. Together, our data strongly suggest that ATV and ATV/RTV should be considered among the candidate repurposed drugs undergoing clinical trials in the fight against COVID-19.