Sunderland have agreed terms with Central Coast Mariners for the transfer of Nectarios Triantis.
The 20-year-old central defender is expected to join the Black Cats for an initial fee of £300,000.
Triantis is an Australia Under-20 international who is expected to move up to their under-23 squad this summer.
Triantis played 25 times for the Mariners and started as they beat Melbourne City in the A-League grand final at the weekend.
Sunderland are looking to reinforce their squad after reaching the play-offs in their first season back in the Championship for five years.
They suffered problems with injuries to central defenders at key moments of the season with Danny Batth, Dan Ballard and Aji Alese all missing for lengthy periods.
"The opportunity to join such a prestigious club is an honour and I'm really looking forward to heading to England and meeting my new teammates later this month," Triantis said.
"I'm ready for the challenge ahead and can't wait to get started. I would like to thank Nick Montgomery and the Central Coast Mariners for giving me the platform that led to this exciting next chapter in my life."
The transfer is subject to international clearance and cannot be completed until the transfer window opens next Wednesday.