Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and other SARS-like-CoVs encode 3 tandem macrodomains within non-structural protein 3 (nsp3). The first of these macrodomains, termed Mac1, is conserved throughout CoVs, binds to mono- and poly-ADP-ribose, and hydrolyzes mono-ADP-ribose (MAR) from target proteins. Mac1 is essential for pathogenesis in multiple animal models of CoV infection, implicating this domain as a prominent virulence factor and potential therapeutic target. Mac1 likely counters host-mediated antiviral ADP-ribosylation, a posttranslational modification that is part of the host response to viral infections. Here we report the crystal structure of SARS-CoV-2 Mac1 in complex with ADP-ribose refined at 2.2 Å resolution. SARS-CoV-2, SARS-CoV and MERS-CoV Mac1 exhibit similar structural folds and ADP-ribose binding modes as shown by structural comparison. All three CoV Mac1 proteins bound to ADP-ribose with low μM affinities. They also demonstrated highly efficient de-MARylating activity, which was greater than that of the human Mdo2 macrodomain. We conclude that the SARS-CoV-2 and other CoV Mac1 proteins are highly efficient ADP-ribosylhydrolases with strikingly similar activity, indicating that compounds targeting CoV Mac1 proteins may have broad antiviral activity against CoVs.