Kirk was 9-1 with a 0.45 ERA at Owasso (Okla.) High School, striking out 111 batters. In three seasons, he went 23-1 with a 1.38 ERA and 224 strikeouts.
With the addition of Kirk, the Cubs have agreed to terms with 26 of their 50 selections from the Draft, including nine of their first 10. The only player unsigned is left-handed pitcher Brooks Raley, who was selected in the sixth round out of Texas A&M.
Kirk was assigned to the Cubs' Rookie League team in Mesa, Ariz.
Meanwhile, infielder DJ LeMahieu, the Cubs' second-round pick out of LSU, was to join Class A Peoria on Tuesday. LeMahieu helped the Tigers win the College World Series.
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.