The 22-year-old loosehead prop made his debut for Connacht against Benetton Treviso in September 2011 and has since graduated from the Connacht Academy.
He made a big impact in a number of Connacht's major games last season, standing out against European powerhouses Toulouse and playing his part in the famous Heineken Cup victory over Harlequins at the Sportsground.
With 20 Connacht caps to date, Buckley has made an appearance in all but one game this season including both Heineken Cup pool fixtures, in which he was picked to start against Zebre and Harlequins.
Commenting on his contract extension with the westerners, he said: "I'm delighted to have signed for another two years; it is such a privilege to play for your province.
"Connacht are achieving more and more each year and I'm really looking forward to being part that and making my mark."
Connacht Rugby CEO Tom Sears added: "Our aim is to build the strongest squad possible and Denis' signing ensures that we are en route to doing so.
"He has truly played his part this season and we're delighted to announce that he will continue to do so over the coming seasons."