Glasnow, one of the Pirates' top pitching prospects, posted a 5.65 ERA in five appearances this spring, but Hurdle cited the right-hander's "ceiling" as a factor in his decision.
"There's going to be some growing pains along the way," Hurdle told reporters, according to MLB.com. "However, what he can bring to the table and how that can play out, there's a ceiling there that's significant.
"We need to help that development. I think we all believe the best opportunity for development is at this level now."
Glasnow will join Gerrit Cole, Jameson Taillon, Chad Kuhl and Ivan Nova in Pittsburgh's rotation after beating out Trevor Williams for the No. 5 spot. Hurdle informed both Glasnow and Williams of his decision after the Pirates' exhibition game Friday in Montreal against the Toronto Blue Jays.
"I was extremely excited when they told me," Glasnow said. "It's great. It was honestly really exciting."
Glasnow, 23, pitched a 1.87 ERA at Triple-A Indianapolis last year but had a hard time adjusting to the majors in his first taste, going 0-2 with a 4.24 ERA in seven appearances with the Pirates.
The 6-foot-8 Glasnow was rated earlier this year as the Pirates' second-best pitching prospect and the No. 25 overall in baseball by ESPN's Keith Law.
The Associated Press contributed to this report.