Ehud Barak, Israel's defence minister, says he is leaving politics and will not run in January elections.
Barak, who is also a former prime minister, says he will stay on in his current post until a new government is formed following the January 22 balloting.
Barak, who served as Israel's prime minister between 1999 and 2001, said he would now concentrate on his personal life.
"I want to study, to write, to live and have a good time," he told reporters.
Al Jazeera's Tom Ackerman, reporting from Jerusalem on Monday, said there were doubts that Barak's Atzmaut (Independence) party would survive the next election.
Most opinion polls showed the party not clearing the threshold to win any seats in the Knesset, or parliament. So it is quite probable that Barak resigned now in order to save face.
He said he has been wrestling with the decision for several weeks but wanted to spend more time with his family.
Barak oversaw the Labour party's decline from 19 seats to 13 in the Knesset under his leadership.
He faced criticism for bringing the left-leaning Labour into Binyamin Netanyahu's conservative cabinet after the last election, a move that granted him a political future as defence minister.
Barak and Netanyahu, who enjoyed a close working relationship for most of the past four years, reportedly have fallen out over whether to defer to the US on any attack against Iranian nuclear facilities.
Barak's detractors in Netanyahu's Likud Party wanted him replaced.
Last year, Barak broke away from Labour, taking with him four Knesset members to form Atzmaut.
However, the question of him leaving politics has arisen before, back in 2000, Al Jazeera's Ackerman said, adding that it was not out of the question that he would come back.
Barak served in the Israel Defense Forces for 39 years, rising to become the Chief of General Staff for four years from 1991 to 1995.
He served with distinction in the 1973 Middle East war and oversaw two operations to free Israeli hostages on hijacked planes.
Barak led the 1972 operation against Palestinian fighters from the Black September group who had seized a Sabena flight and forced it to land in Israel.
In 1976, Barak led the raid on Entebbe airport in Uganda to rescue another plane of Israelis also being held hostage by Black September.