Already tied to the club for the upcoming campaign, Appiah-Kubi will now remain with the Wanderers until the end of the 2014/15 season.
The pace winger made a strong impact in his debut A-League season, making 13 appearances for Tony Popovic's side including the grand final defeat to Central Coast.
"Kwabena is an outstanding prospect and a player we are very keen to continue working with and developing," Popovic said.
"He's got speed, great skills and is dedicated to improving every day at training.
"We had him locked in for a second season but as you put time and energy into a player you need to make sure you look after your investment.
"I've said from the beginning what an exciting young player Kwabena is.
"He's developing well at the club and is proving every day what a good professional he is."
With his immediate future now secured, the 21-year-old is now hoping to secure more game time this season.
His signing comes just two days after leading attacker Mark Bridge penned a three-year extension for the club, in a huge boost just over a month out from the new season.
"It's one of the major goals I set before the start of pre-season to get re-signed and I was hoping for it towards the end of the season but it's obviously come now and 'Popa' has already shown a lot of faith in me so I was very happy to re-sign," Appiah-Kubi said.
"Being in last year's Hyundai A-League Grand Final not only gave me confidence on the pitch but it gave me confidence off the pitch and that is what I am trying to show now."
The Wanderers open their season with a grand final rematch against the Mariners in Gosford on October 12.
