Royals signed Vaibhav Suryavanshi, from India's northern state of Bihar, for $200,000 in the player auction in Saudi Arabia.
The youngster came to the limelight last month when he scored a century against Australia's Under-19 team off just 58 balls.
At the age of 13 years and 187 days, Suryavanshi broke the record of Bangladesh's current Test captain Najmul Hasan Shanto, who at the age of 14 years and 241 days held the previous record of scoring a century at youth level.
Delhi Capitals also showed plenty of interest when bidding for Suryavanshi started before Rajasthan eventually bought him.
Vaibhav Suryavanshi walks out to bat for Bihar during an Indian Ranji Trophy match in Patna. (AP PHOTO)
"He's (Suryavanshi) been to our high performance centre in Nagpur, he had trials there and really impressed our coaching set-up there," Rajasthan's chief executive officer Jake Lush McCrum said.
"He's an incredible talent, we are really excited to have him as part of the franchise. Of course you've got to have the confidence he can step up to the IPL level."
McCrum, who said of the team's signing policy, "you want players on the bench who are hungry", added: "lots of work will go into the coming months to continue to develop (Suryavanshi)." The IPL begins on March 14.
Suryavanshi's century was followed by scores of one and three against Australia's youngsters. He has since batted in four first-class matches for Bihar making 4, 6, 5, 41, 13 and 0, plus 13 in a T20 at the weekend.
Suryavanshi idolises legendary West Indian batter Brian Lara and often gets tips from former Indian batter Wasim Jaffer, with whom he met during an Under-19 tournament in Bangladesh last year.
His father Sanjiv Suryavanshi is his coach and has worked with him since an an early age once his son started to show interest in the game.
"He is not just my son now, but entire Bihar's son," the elder Suryavanshi told Press Trust of India. "My son has worked hard."
Ness Wadia, co-owner of rival team Punjab Kings, said of the signing: "That is what the IPL is about, making dreams come true."
