Koroibete signed a two-year extension in a huge boost for the Wallabies ahead of their Rugby World Cup campaign starting against Fiji on Saturday.
The 27-year-old made his Test debut in 2017 and has amassed 24 appearances, scoring nine tries.
"I am really enjoying my rugby, so it was an easy decision to stay with a club [the Rebels] that gave me a chance to play the game," the Fiji-born Koroibete said in a statement on Friday.
"My family and I are very happy in Melbourne and we have support at the Rebels that is not taken for granted.
"I still have a lot that I want to achieve in rugby and after the World Cup I am excited to get back to the Rebels and do our best to play Super Rugby finals in 2020."
A former NRL star, Koroibete made the switch to union by leaving Melbourne Storm for the Rebels ahead of the 2017 season.
He has made 41 Super Rugby appearances for the Rebels, scoring 16 tries.
The Wallabies are in Pool D at the Rugby World Cup and will face Wales, Uruguay and Georgia after their clash against Fiji.