Last season, the Irishman made 18 appearances in the Championship - all of which came in the second half of the campaign - and he has been rewarded with a fresh deal at Loftus Road.
The 21-year-old told the club's official website: "I am absolutely delighted to have signed an extension.
"It's great reassurance for me. Hopefully, in the next three years, we can build something, start finishing at the right end of the table, and then get back to the Premier League.
"It's been seven months since I made my debut, and it's a crazy story really when you think about it. To come from Ireland and playing in the League of Ireland to playing regularly in the Championship like I was last season, it's something I am definitely proud of."
QPR ended last season in 18th position, but they won nine of their 23 matches after Manning was handed his debut on New Year's Eve.