If confirmed, he would replace Leon Panetta as defense secretary.
Obama said Panetta, standing with the others alongside the president, had "earned the right to return to civilian life."
Panetta was CIA director before Obama tapped him to be defense chief.
Along with secretary of state nominee Sen. John Kerry, D-Mass., Hagel and Brennan would play key roles implementing and shaping Obama's national security priorities in a second term. All three men must be confirmed by the Senate.
In nominating Hagel, Obama signaled he is willing to take on a tough confirmation fight. Once Hagel emerged as Obama's likely nominee, GOP lawmakers began sharply questioning his commitment to Israel and his willingness to take a hard line with Iran over its disputed nuclear program.
Of Brennan, Obama said he had an "invaluable perspective" on global affairs. He has traveled extensively in the Middle East and was once CIA station chief in Saudi Arabia. Brennan helped orchestrate administration policy in Yemen and the response to the Arab Spring, and played a role in the raid that killed Osama bin Laden.
"I will make it my mission to make sure that the CIA has the tools it needs to keep our nation safe and that its work always reflects the liberties, freedoms and values that we hold so dear," Brennan said in brief remarks.
Sen. John McCain, R-Ariz., issued a statement shortly after the White House announcement on Brennan, saying he had "many questions and concerns about his nomination to be director of the Central Intelligence Agency, especially what role he played in the so-called enhanced interrogation programs while serving at the CIA during the last administration, as well as his public defense of those programs."
Hagel, something of a maverick among Republican senators during his two terms, has criticized the discussion of a military strike by either the U.S. or Israel against Iran. He also irritated some Israel backers with his reference to the "Jewish lobby" in the United States. And he has backed efforts to bring Iran to the table for future peace talks in Afghanistan.