Benjamin Netanyahu has been asked to form the next Israeli government by President Shimon Peres.
The Likud leader met the head of state this afternoon to receive a formal invitation to head the next administration.
Mr Netanyahu immediately called for a broad, national unity coalition with centrist and left-wing partners.
His nomination was a break with Israeli tradition, which has always given a governing mandate to the leader of the first-placed party.
Mr Netanyahu urged his opponents to close ranks for the sake of the country and join his government.
He said: 'I call on Kadima chairwoman Tzipi Livni and Labour Party chairman Ehud Barak and I say to them: let's unite to secure the future of the State of Israel.
'I ask to meet with you first to discuss with you a broad national unity government for the good of the people and the state.'
Mr Netanyahu, who was prime minister in the 1990s, has six weeks to forge a coalition cabinet.
Mr Peres met separately earlier in the day with Mr Netanyahu and Ms Livni to try persuade them to form a unity government.
Both laid claim to the premiership after Kadima won 28 seats to Likud's 27 in the 120-member parliament following the 10 February election.
Ms Livni hinted after her meeting with Mr Peres that her position had not changed. She was not prepared to join a national unity coalition with the Likud leader unless she was prime minister.
'It would be a coalition that doesn't allow me to pursue my path, the path of Kadima as we promised the voters', she said.
'A large government has no value if it does not have a path. The decision is now in the president's hands.'
Asked if she was ready to go into opposition she said: 'If necessary, certainly.'
