Moriarty, a Grand Slam winner with Wales in 2019, joined Dragons in 2018 following his switch from Gloucester Rugby.
Welcoming the news, Director of Dragons Rugby Dean Ryan said: “We are delighted to retain Ross’ services at Dragons.
“His decision to renew his contract shows that he is committed to and believes in what we are doing here.
“More importantly, he also feels we can help him achieve his ambitions over the next couple of seasons.”
The 25-year-old is an almost ever-present member of the Welsh back row and scored the winning try as Wales narrowly defeated France to make last year’s Rugby World Cup semi-finals.
“I’ve enjoyed the last season with Dragons and everyone can see we are moving in the right direction,” said Ross.
“We had some good results this season and I feel we will push on when we start playing again. I can’t wait to get back to playing at Rodney Parade, the atmosphere we had for the derby games this season was really special.
“Dean has made a big difference since he joined and he has got me enjoying my rugby again which has followed into my international games, even if we didn’t get the results we would’ve liked.”
Moriarty’s re-signing follows Ollie Griffiths, Rhodri Williams, Jordan Williams, Josh Lewis and Rio Dyer in committing for next season and beyond.
Academy products Taine Basham, Max Williams, Connor Edwards, Lennon Greggains, Josh Reynolds and Dan Babos also agreed new terms earlier this season.