Defence Minister Ehud Barak, a main architect of Israel's policy towards Iran's nuclear programme, said in a surprise announcement on Monday that he was quitting politics and would not run in the January 22 national election.
"I have decided to retire from political life and not to run for the next Knesset ... I will end my term as defence minister once the next government is established, in about three months," he told a news conference.
"I want to dedicate more time to my family. I feel I have exhausted dealing with political life, which has never been a passion of mine, and I feel there is room to allow other people to serve in senior roles in Israel," he said.
Opinion polls had predicted a poor showing for the small party that Barak currently leads, Atzmaut, but recently indicated voter support had strengthened as a result of Israel's eight-day offensive in the Gaza Strip that ended in a ceasefire on Wednesday.
Barak, 70, has been a key player in Israel's tough policy towards curbing Iran's nuclear ambitions and a pointman in the Jewish state's strategic relations with the United States.
He has been defence minister since 2007 and served as prime minister from 1999 to 2001.