"During consultations with party representatives, 54 lawmakers supported Benny Gantz to form a government. Therefore, today I give him the mandate to form a government coalition ... There is little time left and we are facing serious challenges," Rivlin said at an official ceremony broadcast by Israeli television.
"There are no excuses and serious reasons to hold the third election", the president stressed and wished Gantz good luck in forming the government.
Prime Minister Benjamin Netanyahu earlier handed back the mandate to Rivlin after he failed to form a majority coalition within a 28-day deadline, which was granted to him after the 17 September general election.
In the vote, Blue and White won 33 seats, while Likud came in second place with 32. Gantz has refused to enter coalition talks with the prime minister, leading to another deadlock in the Knesset.