Lille had confirmed the Frenchman was in discussions with another club, with the Italian press reporting he had been in talks with Roma president James Pallotta in New York.
Now the 49-year-old has been formally unveiled as the new coach of the Giallorossi in a deal worth a reported 1.5million euros per season.
"A.S. Roma announces that it has reached an agreement with Rudi Garcia, who will become the head coach of the first team," said a statement on the club's official website.
"The two year contract will be formalised and deposited in the upcoming days."
Garcia, though, will face immediate pressure.
Former coach Zdenek Zeman was sacked in February with interim boss Aurelio Andreazzoli then failing to secure European football as the team finished sixth.
To rub salt into the wounds, Roma then lost the Coppa Italia final to arch-rivals Lazio.
However, Garcia has already demonstrated the pedigree that attracted Roma by guiding Lille to the Ligue 1 title and Coupe de France in 2011.
Pallotta said: "We are very excited and confident that Rudi Garcia is the right coach for AS Roma.
"He is a proven winner with a great football mind who we believe fits in perfectly with our vision for the future."
"We welcome Rudi Garcia to AS Roma. "
Chief executive Italo Zanzi added: "He will continue to develop our existing talent base while giving us the best opportunity to win now. We are looking forward to this season more than ever."