In April this year, the 21-year-old was looking to leave the Red V due to his limited playing time under axed Dragons coach Shane Flanagan.
But since Flanagan's exit the prop has gone on to become a mainstay of the youthful pack deployed by Dean Young.
Pasifiki Tonga has played 13 games this season and been elevated to a starting front-row berth under Young.
"I'm really excited to be extending my time here at the Dragons under Dean Young," Pasifiki Tonga said.
"I've been enjoying my footy and I believe in the direction that Youngy is taking us.
"I've been at the Dragons since I was 17 years old; I've grown up here and I've built a lot of relationships. I love my teammates and I'm confident that we are on the way up here."
Pasifiki Tonga joins Hamish Stewart, the Couchman brothers, Ryan and Toby, and Dylan Egan in committing to the Dragons on long-term deals, creating hope that a core of young forwards can help turn the club around and end their finals drought.
"Extending Loko was a priority for the club and we're thrilled to have got it done," said Dragons chief executive Tim Watsford.
"We've made a deliberate effort to invest in our pathways and Academy programs.
"Players such as Loko, Hamish, Dylan, Ryan and Toby are the result of this investment and it gives us confidence that this club's identity continues to be shaped around homegrown talent."
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