He wrote: "The state of Israel, the army and the security establishment are experiencing a major shake-up. I believe that I possess the capabilities and talents necessary to serve as Israel's next defence minister."
The next leader of the Labour Party will also likely become defence minister. Barak's military pedigree could give him an advantage as Israel recovers from the war while facing a potential nuclear threat from Iran.
In security-obsessed Israel, the defence ministry could serve as a springboard to the premiership.
As Israel's most-decorated soldier, Barak participated in wars and daring commando raids. He retired from the military in 1995 at the end of his term as chief of staff.
Joining the Labour party, he was quickly appointed to the cabinet.
In 1999, he was elected prime minister, also serving as defence minister.
But his term lasted less than two years - the shortest for an elected premier - and he left office under stiff public criticism for his unilateral withdrawal from south Lebanon in 2000 and his offers of far-reaching concessions to the Palestinians and Syrians that failed to result in peace deals.
He was defeated in a 2001 election by Ariel Sharon.
Hanan Crystal, a political commentator, said the war in Lebanon - and the public sentiment that Israel's military must regain its might - has restored Barak's political status.
"We need a defence minister, and everyone knows he is more suitable than anyone else," he said. "He is an authority. There will be a feeling that 'the boss is back' ... no one ever argued about his abilities, but he has other problems."