Seven of the top 10 Rangers picks have been signed, including the top four.
Ortiz, a 6-foot-3, 220-pound righty, was 5-3 on the season with a 1.04 ERA. He had 72 strikeouts in 43 2/3 innings.
"[Scout] Butch [Metzger] did a heck of a job with Luis and his family," said Rangers director of amateur scouting Kip Fagg. "We feel that we got a very powerful young man -- right-handed pitcher with good stuff."
Assistant general manager A.J. Preller said the Rangers were pleasantly surprised when Ortiz was still on the board at No. 30.
"Luis was a guy, I think, that was on the national scene we saw last summer," Preller said. "He was a guy we were hoping we'd get a chance to select."
Ortiz -- originally a Fresno State commit -- was a closer for the 18-and-under USA Baseball national team that won a gold medal. He is also a World Cup MVP award winner. MLB.com rated Oritz as the No. 24 overall prospect in the Draft.
He'll graduate from high school Saturday, and then begin in the Arizona Rookie League.
"It means the world to me now," Ortiz said. "It's just a start and I'm getting ready to play professional baseball. ... No more high school now."
Oritz has mentioned that he never has had a true pitching coach, but that he tried to model himself after Felix Hernandez of the Mariners. During the offseason, Ortiz worked with former Ranger Matt Garza, who is currently 4-4 with the Brewers.
"He taught me a lot about the steps and how to handle failure," Ortiz said. "He's like an older brother to me."
Ortiz said he showed his commitment to baseball and playing professionally when he lost 45 pounds in high school. He trimmed down to 205 pounds from 250, and then gained 15 pounds of muscle working with Garza.
He's thrilled about the next step.
"I'm ready to leave [home]," Ortiz said. "[I'm] 18, time to start life. It's my job now."