It was a blow to Netanyahu, who is fighting for his political life amid unprecedented political deadlock and a criminal indictment for corruption, which he denies.
But it remains unclear whether Gantz’s centrist Blue and White Party can break a stalemate that has been marked by three inconclusive elections in less than a year.
Netanyahu, 70, is Israel’s longest-serving leader and has been heading the country’s efforts to combat the coronavirus.
But last year he twice tried unsuccessfully to put together a ruling coalition.
And on Sunday Gantz won support from two key parties, leading President Reuven Rivlin to say that he would get the first chance at forming a government after the latest election on March 2.
“Tomorrow, around midday, the president will assign the task of forming the government to head of (Blue and White party) Benny Gantz,” Rivlin’s office said in a statement.