Griffiths has made 70 appearances for the Dragons – scoring four tries – and has played four games this season.
The 24-year-old has one Test cap for Wales to his name which came against Tonga in Auckland in June 2017.
He was involved in Wayne Pivac’s first Wales squad which faced the Barbarians last month as a substitute although that game was a non capped international.
A product of the Dragons Academy, the Newbridge-born Griffiths made his debut for the Dragons against Ulster in 2014.
Director of Dragons Rugby, Dean Ryan, said: “Extending Ollie’s contract with us is a big boost as he forms an important part of our group. He is committed to what we are trying to achieve in the region.
“He is an example of a local rugby player who came into our academy, worked hard, and ultimately has gone on to represent both his home region and nation.
“We are looking forward to continue working with him and I am sure the crowds that come to watch the Dragons will be pleased to see him staying with us.”
Griffiths said: “I feel we are building something really good at the Dragons and the progress we have made in the last six months made the decision easy for me.
“I’m excited for the future and look forward to seeing us repay our fans for their loyal support and sticking by us through some difficult times in the past.
“The Dragons is definitely the best place for me to continue my development.
“Playing for my local region every week, with players I have come through the academy ranks with, makes it a special place for me.”
