Hagel began his opening statement by saying he was humbled by the decision to nominate him as the nation's defense secretary.
Hagel pledged he would always give President Obama his most informed and honest advice, and that national security would be his first and foremost priority in any situation.
And he went on the offensive against senate Republicans who claim Hagel would pursue a strategy of "appeasement" against America's enemies and abandon Israel, saying that his previous remarks that he was "an American senator, not an Israeli senator" did not indicate he held any anti-Israeli beliefs.
"No one individual vote, quote, or statement defines me, my beliefs, or my record," Hagel said.
"My overall worldview has never changed: that America has and must maintain the strongest military in the world; that we must lead the international community to confront threats and challenges together; and that we must use all tools of American power to protect our citizens and our interests. I believe, and always have, that America must engage -- not retreat -- in the world. My record is consistent on these points," he continued.
Contesting critics who say he is soft on the Iranian nuclear program, Hagel said that "my policy is one of prevention, and not one of containment - and the president has made clear that is the policy of our government."
Hagel promised to keep the military strong even if Congress cuts the defense budget.
"I am committed to effectively and efficiently using every single taxpayer dollar; to maintaining the strongest military in the world; and to working with Congress to ensure the department has the resources it needs -- and that the disposition of those resources is accountable."
If confirmed, Hagel will be the first enlisted person to serve as Defense Secretary. He was a decorated sergeant in the Army during the Vietnam War.