Selman, a left-handed pitcher out of Vanderbilt, is the teams' last remaining top-10 pick that has yet to sign.
In 17 games with the Commodores this season, Selman went 9-3 with a 3.55 ERA. He struck out 80 batters and walked 43 over 76 innings pitched.
Additionally on Wednesday, the Royals announced the signing of their fourth-round pick, Stanford shortstop Kenny Diekroeger. Diekroeger was drafted in the second round of the 2009 Draft by Tampa Bay, but he passed on a contract to play for the Cardinal.