Talented young Australian defender Nectarios Triantis has signed with English Championship club Sunderland for an undisclosed fee from Central Coast Mariners.

Triantis, 20, had only played seven minutes in the A-League Men with Western Sydney when he joined the Mariners ahead of last season but quickly became a crucial part of the team that won a fairytale championship.

The central defender made 26 appearances, starting all but four of those matches, and earned selection on the bench in the PFA team of the season.

Triantis is poised to join Bailey Wright at Sunderland, though the Socceroos veteran was loaned out to fellow Championship outfit Rotherham for the second half of last season.

His departure is a hefty blow for ALM champions Central Coast, who are also bracing for the departure of striker Jason Cummings to Indian club Mohun Bagan.

"Whilst we are obviously sad to be losing Nectar, we are so happy for him to be given this opportunity to join such a fantastic club like Sunderland," coach Nick Montgomery said in a statement on Thursday.

"We would never hold him back from a move like this as he deserves it.

"Their fans are amazing and it's a massive club. I have no doubt with time he will become a fan favourite for them.

"He is a wonderful young man who has developed rapidly in 12 months and played a vital role in helping us win the championship this season.

"When we lost Kye Rowles last season we needed someone to fill big shoes and Nectar certainly did that.

"It's now time for him to make us all proud and I have no doubt he can be representing the Socceroos at the next World Cup."

The young defender follows Rowles and Garang Kuol in netting a hefty transfer fee for the Mariners in recent years.

Triantis played in this year's under-20 AFC Asian Cup with the Young Socceroos and is currently with the Olyroos at the Maurice Revello Tournament in Toulon, preparing for qualification matches for the Paris 2024 Olympic Games.