The testimony on Thursday comes amid a string of scandals that have left his coalition teetering.
The beleaguered Olmert became the last in a string of about 70 senior political and military officials to testify before the commission since it was set up in September.
Güncelleme Tarihi: 20 Eylül 2018, 18:16
The commission, headed by Eliyahu Winograd, a retired judge, is due to present its findings in the coming weeks.
It was set up amid a chorus of public criticism of the country's leadership in the wake of the 34-day war in Lebanon that failed to achieve its main goals of freeing two captured Israeli soldiers and stopping Hezbollah rocket fire.
Should the commission find Olmert directly responsible for the perceived failures of the war, it will be the latest blow to strike the premier whose ratings are falling to single digits amid a string of scandals involving him and senior members of his government.