The 50-year-old took charge at the Stadio Olimpico last summer and led Roma to a hugely successful Serie A campaign in 2013-14 as they finished second behind champions Juventus to secure a return to the Champions League.
The Frenchman's previous deal was due to expire in June 2015, but he has now agreed on a three-year extension to his contract to tie him to the club until the end of the 2017-18 campaign.
"I am happy to announce that Roma and Rudi Garcia have reached an agreement for the extension of his contract by an additional three years," president James Pallotta told the club's official website.
"Having spent the first half-hour in Rudi's company in New York, I knew he would be the right man to lead Roma for a long time.
"This extension is an integral part of our plan to bring continuity and success to the entirety of our project. The owners of Roma, and its leaders, have worked hard to build a world-class team. This is another step towards fulfilling our long-term programme.
"We are only at the beginning of our journey and I want once again to thank Rudi, his staff and all of Roma for a wonderful beginning to what I hope will become a great future for all Giallorossi fans around the world."