The club did not disclose terms of the contract, but it was believed the deal was for a guaranteed $3 million plus incentives. Crow will go on the Royals' 40-man roster and be invited to Major League Spring Training next year.
"He's a tremendous competitor and he's got a chance to be a quality Major League starter," general manager Dayton Moore said.
The Royals will introduce Crow at a news conference at 2:20 p.m. CT on Friday at Kauffman Stadium in Kansas City.
J.J. Picollo, assistant general manager in charge of scouting and player development, said the Royals pushed to get the deal done so Crow could report to the Arizona instructional league on Sunday. The league begins on Monday.
"It was important for Aaron to get out and play," Moore said. "He was drafted by his boyhood team and he wanted to get out and pitch. He wanted to get out and go."
Crow, from the University of Missouri and Wakarusa, Kan., in the Topeka area, was the 12th overall pick in this year's Draft. He was drafted in 2008 by the Washington Nationals but did not sign, reportedly turning down a $3.5 million offer.
He was not subject to the Aug. 17 signing deadline this year because he had played independent pro ball and had no college eligibility remaining. Major League Baseball ruled that he and first-round supplemental pick Tanner Scheppers were exempt.
That relieved the Royals of deadline stress -- they had gone to the final minutes to sign 2007 first-round pick Mike Moustakas and '08 first-round Eric Hosmer -- and negotiations with Crow continued.
"J.J. and the guys did a tremendous job," Moore said. "It completes our 2009 Draft and we feel very good about it, and we feel like we're continuing to fill our pipeline."
In 2008 for Missouri, Crow was the Big 12 Conference Pitcher of the Year and a Golden Spikes Award finalist after going 13-0 with a 2.35 ERA in 15 starts. He had 127 strikeouts and logged 43 consecutive scoreless innings that season.
He throws a mid-90s fastball, a sharp slider and a changeup.
"He looks in good shape. He's been throwing in side sessions in the bullpen," Moore said.