According to a statement released by the Gosford club, the 24-year-old has signed a pre-contract agreement and will leave to attend a training camp in Japan this week.
Duke won the 2012-13 A-League title with the Mariners and has earned four caps for the Socceroos.
“I came through the youth stages of the Mariners for two years and was rewarded with a first team contract, so my time at the Mariners has been unbelievable," he said.
“I’ve signed a pre-agreement deal and I’ll be going over to Japan on Tuesday to complete a medical so once the medical clears up I’ll be signing a full contract.
“The J-League is a well-respected league all around the world, all you have to do is take a look at the Japanese national team to see the quality players the J-League can produce. I’ve got to work my ass off and it’s a huge challenge for me to head overseas and prove myself in another country."
Mariners coach Phil Moss acknowledged the loss of Duke is a blow to the club, but backed the young centre-forward to succeed in Japan.
“It always gives us as a club, playing and coaching staff great pleasure to have played a role in helping a young player develop his game to a point where it attracts interest from big leagues and the J-League is arguably the biggest in the Asian region," he said.
“Mitchell Duke is the next Mariners player to come off the club’s production line and now gets his chance overseas. The timing is never great when you lose a key player mid-season but it gives other players the opportunity to step up and of course, we have Fabio Ferreira ready to go this week.
“It’s a great opportunity for ‘Dukey’ to take his career to the next level and he goes with our blessing."
Duke won the 2012-13 A-League title with the Mariners and has earned four caps for the Socceroos.
“I came through the youth stages of the Mariners for two years and was rewarded with a first team contract, so my time at the Mariners has been unbelievable," he said.
“I’ve signed a pre-agreement deal and I’ll be going over to Japan on Tuesday to complete a medical so once the medical clears up I’ll be signing a full contract.
“The J-League is a well-respected league all around the world, all you have to do is take a look at the Japanese national team to see the quality players the J-League can produce. I’ve got to work my ass off and it’s a huge challenge for me to head overseas and prove myself in another country."
Mariners coach Phil Moss acknowledged the loss of Duke is a blow to the club, but backed the young centre-forward to succeed in Japan.
“It always gives us as a club, playing and coaching staff great pleasure to have played a role in helping a young player develop his game to a point where it attracts interest from big leagues and the J-League is arguably the biggest in the Asian region," he said.
“Mitchell Duke is the next Mariners player to come off the club’s production line and now gets his chance overseas. The timing is never great when you lose a key player mid-season but it gives other players the opportunity to step up and of course, we have Fabio Ferreira ready to go this week.
“It’s a great opportunity for ‘Dukey’ to take his career to the next level and he goes with our blessing."