Tiatia began his career with Wellington in New Zealand before moving to Japan and then joined Ospreys in 2006.
He had four hugely successful seasons as a player at Ospreys, twice winning the Magners League, before spending a year as assistant coach.
Tiatia was a fearsome competitor on the pitch, and Dragons head coach Dai Flanagan hopes he will bring a new edge to his side, who have one of the worst defences in the United Rugby Championship.
“Filo returns to Wales with a wealth of coaching experience and is an innovator and leader in every sense of the word who will make a huge impression here,” said Flanagan.
“There is no doubt he will grab this role with both hands and stamp his mark on it.
“I have always stated it shouldn’t be easy when teams come to Rodney Parade or face the Dragons and I know Filo will work with our squad to rebuild that area of our game and make it his very own.
“I have no doubt that Filo will be a great ally and I know how keen he is to come back to Wales and become a Dragon.”
