"Graham Arnold and the coaching staff has been working hard to identify key talent both here in Australia and overseas, and Rostyn arrives with a strong football pedigree," said Mariners executive chairman Lyall Gorman.
"We look forward keenly to the contribution we hope Rostyn will make to the Mariners, both on and off the field."
Griffiths has appeared in Mariners colours previously, trialling during a pre-season tour to Queensland last July.
"Rostyn is a really good signing for us," said Arnold. "I was impressed with him at North Queensland Fury, especially as a central defender.

"He can also play defensive midfield but every time he has played central defence they have kept a clean sheet.
"He's a natural defensive midfielder so he's very good on the ball but his positioning we will work on him tactically, but I think Mariners supporters will see a lot from him.
"Lawrie and I both watched him closely throughout the season and he's been very impressive. He's tall, he's strong, and he can play in a number of positions. He is solid in defence but can get forward as well, and hopefully he'll prove very useful for us next season."
The 22-year-old says he liked what he saw from his brief stint with the Yellow and Navy, and is keen to rekindle the association.
He added: "It's a really well run club, and being around the boys on trial last year was a great experience so it'll be nice to go back there.
"I'm thankful to Fury for my time there, but this is a good opportunity for me, and I'm looking forward to working under Graham Arnold and hopefully helping the Mariners to some silverware."