He was placed on the Reds 40-man roster after the 2010 season, but was optioned to Louisville on March 21, 2011. Cozart enjoyed a hot start to 2011, hitting .310/.357/.467 through his first 77 games. He went 100-for-323 with 26 doubles, two triples, seven homers, and 32 RBIs, along with nine steals. The Reds shortstops, Paul Janish and Édgar Rentería, were hitting a combined .226 with one homer and 29 RBI through July 6, and Reds fans everywhere were calling for a change at shortstop. On July 7, 2011, less than 24 hours after an article on Reds.com said there would be no transaction, the Reds optioned Janish and recalled Cozart. Switching uniform numbers from #60 to #2, Cozart started that night at Milwaukee, playing shortstop and batting seventh. In his debut game, he went 1-3 with a run scored. Cozart hit his first home run in the eighth inning off of his college teammate Lance Lynn, on July 17, against the rival Cardinals. He had 10 hits in his first 25 Major League at bats, and at least one hit in each of his first 6 games.