Caerleon-born O’Brien came through the Dragons Academy system and went on to make 70 appearances, scoring 305 points for the region, before leaving to join the Scarlets in 2018.
A former Wales Under-20 international, O’Brien brings a wealth of experience and versatility as he makes a welcome return to Rodney Parade.
Dean Ryan, Director of Dragons Rugby, said: “Angus is very keen to return to his home region and we’re excited to see the impact he can make with us.
“He returns with a wealth of experience and will give us a different way of playing the game.
“Angus is a talented and versatile player who will really add to the competition we have for the fly half and full back jersey.”
O’Brien – who also represented Wales Sevens at the 2018 Commonwealth Games on the Gold Coast – made 41 appearances and scored 86 points in his four seasons at Scarlets.
O’Brien said: “I’m excited to be returning to Rodney Parade and my home region.
“I’ve loved my four seasons at Scarlets, it’s been a great experience for me and I’ve a learnt a lot that I’ll be able to bring back with me to the Dragons.
“I came through the Academy system at Dragons, grew up with a lot of the players, so to be re-joining those boys and working with them again is an exciting prospect.
“Dragons have moved forward since I have left, and the recruitment has been strong ahead of next season. I can’t wait to be a part of it.”
