Less than a week ago, Barak led an eight-day military offensive against the Hamas militant group that rules the Gaza Strip. The fighting, aimed at ending rocket fire from the Palestinian territory. ended in a fragile truce.
"I didn't make this decision (to leave politics) without hesitating, but I made it wholeheartedly," he told a hastily arranged news conference, saying he had been wrestling with the decision for weeks.
He evaded repeated questions about whether he might agree to serve as a Cabinet minister in an upcoming government, leaving open the possibility that he might still retain an impact on Israeli politics. While most Cabinet ministers also hold parliamentary seats, they do not have to be elected lawmakers, and such appointments have been made in the past.
Barak, 70, made the surprise announcement even after polls showed his breakaway Independence Party gaining momentum after the Gaza campaign.
Despite the bump in the polls, Barak still could have found himself fighting for his political survival once election day rolls around. Surveys before the Gaza operation were unkind to his party, at times showing it polling too weakly to even send a single representative to parliament.
"I feel I have exhausted my political activity, which had never been an object of desire for me. There are many ways for me to serve the country, not just through politics," he said, adding that his decision was spurred in part by his desire to spend more time with his family.
Possible replacements include Vice Premier Moshe Yaalon, a former military chief, and Shaul Mofaz, a former military chief and defense minister, who now serves as chairman of the opposition Kadima Party.
Barak's political career was as turbulent as his 36-year military career was dazzling.