The Royals' farm system was ranked number one in baseball entering the 2011 season, led by Hosmer and another top prospect, third baseman Mike Moustakas. Most baseball critics agreed that the Royals, a team that was known for mediocrity the past two decades, would be a contender within a couple of years, and they had nine prospects in Baseball America's top 100, a record for the publication. Hosmer was ranked as the best first baseman prospect in Major League Baseball prior to the 2011 season. He was also rated the eighth best overall prospect by Baseball America, and the top Royals prospect overall. So much hype was placed on the Royals that general manager Dayton Moore traded the team's best player, Cy Young Award winner Zack Greinke to the Milwaukee Brewers for four top prospects, to focus on the team's future. Hosmer began the season with the Royals Class AAA affiliate, the Omaha Storm Chasers of the Pacific Coast League (PCL). When the Royals purchased Hosmer's contract on May 5, 2011, he was leading the minor leagues with a .439 batting average and the PCL with 43 hits and a .525 on-base percentage.
The Royals recalled Hosmer on May 5, 2011. Veteran catcher Jason Kendall was moved to the 60-day disabled list to make space for Hosmer on the 40-man roster. He made his MLB debut at first base the following day against Oakland Athletics starter Gio González, replacing Kila Ka'aihue. Prior to his debut, Hosmer was being touted by journalists as a "super-prospect" and the "most-hyped" rookie to debut for the Royals since Bo Jackson. The Royals promoted Hosmer before a mid-June deadline in which the Royals could have avoided salary arbitration for an extra year. Hosmer went hitless in two at-bats, striking out twice. He also walked twice and stole a base in a 3–2 loss as the Royals had the second biggest crowd of the season.