Terms were not disclosed Wednesday ahead of an afternoon news conference with Appel and team officials.
The 21-year-old Appel was 10-4 with four complete games and a 2.12 ERA this season. He had 130 strikeouts in 106.1 innings pitched and allowed opponents a .203 batting average.
Appel is an Astros fan who grew up in West Houston before moving to California at the age of 12. The Astros had a chance to draft him last year but instead went with 17-year-old shortstop Carlos Correa from Puerto Rico. Appel slid to Pittsburgh at No. 8 last year but turned down a $3.8 million offer and returned to Stanford for his senior season.
Not this time around.
Houston made the 6-foot-4, 195-pound Appel their top pick and he is expected to fetch about double the amount he passed up from the Pirates. He will be a welcome addition to the hard-luck Astros with his mid-90s (mph) fastball, nasty slider and improving changeup.
"Drafting and signing Mark Appel was a top priority for our organization this year," general manager Jeff Luhnow said. "We are an organization focused on winning championships in the future and we expect Mark to be a big part of that effort."
Astros amateur scouting director Mike Elias said the team believes Appel can become a "mainstay' top the rotation for years to come.