Benny Gantz, a respected former military chief of staff, and centrist politician Yair Lapid said in statements they would form a joint list for the election and rotate as prime minister if they won.
Gantz heads his recently launched centrist Israel Resilience party, while Lapid leads Yesh Atid, which currently has 11 seats in the country’s 120-seat parliament.
Opinion polls have shown the two as the main challengers to Netanyahu, who is expected to win despite corruption investigations into his affairs.
In anticipation of the announcement, Netanyahu orchestrated a merger of far-right parties on Wednesday that could help him build a governing coalition after the ballot.
Since Israel‘s creation in 1948 no one party has clinched an outright majority in the legislature and so post-election coalition-building has determined the composition of governments and who leads them.
Netanyahu, 69, has been in power for the past decade, with Likud at the helm of a parliamentary bloc.
Opinion polls have forecast a Likud victory, with some 30 parliamentary seats, in the April 9 ballot, with Resilience and Yesh Atid each trailing by a wide margin and Netanyahu on track to form a rightist coalition similar to the one he heads.
But the surveys also predicted a much tighter race and a possible upset should Gantz, 59, and Lapid, 55, team up and then form a centrist and left-wing parliamentary bloc larger than a Likud-led alliance.
Moshe Yaalon, a former defence minister, had previously joined Israel Resilience and another ex-military chief of staff, Gaby Ashkenazi, will also join the new alliance, the centrist parties said on Thursday.
Netanyahu’s political future has also been clouded by three corruption cases in which the attorney-general is expected to decide soon whether to accept police recommendations to indict him.
The prime minister is suspected of wrongfully accepting gifts from wealthy businessmen and dispensing favours in alleged bids for favourable coverage in a newspaper and a website.
Netanyahu has denied wrongdoing, saying he is a victim of a left-wing witch-hunt to topple him. His opponents are attacking his record and underlining the need for clean governance.
While Gantz and Lapid worked out their deal, Netanyahu helped negotiate the merger of two far-right parties, Jewish Home and Jewish Power, which could give followers of the late anti-Arab rabbi, Meir Kahane, a stronger voice in politics.
Leaders of Jewish Power have portrayed themselves as successors of the US-born Kahane, who served one term in the Knesset in the 1980s as head of the Kach party.
Kach advocated the “transfer” of Palestinians to neighbouring Arab countries and also called for a ban on intermarriage between Israeli Jews and Arabs.
Kahane’s movement was subsequently banned from Israeli politics as racist. He was assassinated in 1990 in New York by an Egyptian-born American.
(FRANCE 24 with REUTERS, AFP)