Moussaoui is the only person convicted in the United States in connection with the deadly attacks. He will be formally sentenced on Thursday by a federal judge.
The 37-year-old French citizen of Moroccan descent was arrested three weeks before the September 11 attacks and said later that he was meant to pilot a fifth airplane into the White House as part of the plot.
He pleaded guilty to six counts of conspiracy, three of which carried a maximum death sentence.
Moussaoui also said he had no remorse for the September 11 attacks, in which about 3,000 people died.
(compiled from agency reports)