The country's second general elections which were held on September 17 after the first polls in April failed to form a government, have put Netanyahu neck and neck with Gantz, and the two were now vying to build a governing coalition, the BBC reported.
This is the first time since 1992 that an Arab political group has issued an endorsement for Prime Minister.
Faced with yet another deadlock, Israel's President Reuven Rivlin has recommended the new government includes both Gantz's Blue and White Alliance and Netanyahu's ruling Likud party.
Rivlin has said he will do everything he can to avoid a third general election in Israel this year.
In reaction, Aymen Odeh, leader of Joint List, told President Rivlin that the alliance's priority was to prevent Netanyahu from serving another term.
Joint List won 13 seats in the election. If Gantz had the endorsement of all 13 seats, he would still fall short of the 61 seats needed for a majority in the 120-seat legislature.
On September 19, Netanyahu invited Gantz to form a unity government to end the political deadlock.
Gantz, a former Army chief, has previously said he would not join a government with Netanyahu so long as the latter, who has served as Prime Minister for a decade, was facing corruption charges.
The President will announce the chosen candidate on Wednesday, after receiving the official and final results of the elections.
( With inputs from IANS )