Giolito, 21, will make his big league debut Tuesday versus the New York Mets, Baker said.
A need for a starting pitcher arose in Washington when right-hander Stephen Strasburg was placed on the 15-day disabled list due to an upper back strain. He has missed his last two scheduled starts.
Giolito has the opportunity to stick with the Nationals even after Strasburg comes back, however. Baker noted that his role will be taken on a start-to-start basis.
Perhaps the best pitching prospect in the minor leagues, Giolito is currently ranked as the No. 1 overall prospect by MLB.com:
"Giolito has the highest ceiling among Minor League pitchers, boasting an elite fastball that sits mid-to-upper-90s and a 12-to-6 curveball that he throws with power and hard, downer action," according to the website's scouting report.
"His changeup has steadily improved in the past two seasons and his confidence along with it, giving him a legitimate weapon against left-handed hitters."
Giolito has the ability to turn into an ace at the Major League level, but it remains to be seen what type of success he will have coming out of the gate.
Certainly having the talent to pitch at the Major League level, the former 2012 1st round pick has not yet progressed past Double-A and his time there has been anything but spectacular.
In 71 innings with Double-A Harrisburg this season over 14 starts, Giolito is 5-3 with a 3.17 ERA and a 72 to 34 strikeout-to-walk ratio. He has a 3.22 FIP there.