By turns emotional and feisty, Mrs Clinton told US lawmakers yesterday she took responsibility for the incident in which US Ambassador Christopher Stevens and three other Americans were killed, but also defended herself.
She interrupted one senator to contradict him and stressed she did not see requests for additional security to protect the Benghazi mission.
Mrs Clinton cast the incident as part of a long history of such violence as well as the result of regional instability since the Arab Spring of popular revolutions began in 2011.
Senator Bob Corker, a senior Republican, kept up the criticism of the Obama administration, saying the Benghazi attack and the US response displayed "woeful unpreparedness" for the events sweeping the region.
Speaking in congressional testimony delayed by more than a month because of her ill health, Mrs Clinton's voice cracked as she spoke of comforting families who lost loved ones in the attack, the first since 1988 in which a US ambassador was killed.
"For me, this is not just a matter of policy – it's personal," Mrs Clinton told the Senate Foreign Relations Committee on what is likely to be the last day she will testify before Congress before stepping down as Secretary of State.