A US court sentenced Osama bin Laden's son-in-law and former Al-Qaeda spokesman, Sulaiman Abu Ghaith, to life in prison on Tuesday.

The 48-year-old Kuwaiti, who has defended the Sept 11, 2001 attacks, was found guilty on March 26 of plotting to kill Americans and providing material support to terrorists.

Before the sentence was handed down in a US federal courtroom, Sulaiman spoke in Arabic through a translator to say the only judgement he would accept was that of God.

"Today when you are shackling my hands, and intend to bury me alive, you are unleashing the hands of thousands of Muslims and they will join the rally of free men," he said.

Judge Lewis Kaplan said Sulaiman failed to show remorse for the Sept 11 attacks and told the courtroom he remained a menace.

"You continue to threaten," Kaplan said. "What you have done warrants the maximum sentence."

Sulaiman is the highest ranking Al-Qaeda leader ever held in a prison on US soil.

In a Sept 12, 2001 video, he is seen sitting alongside Osama and current Al-Qaeda leader Ayman al-Zawahiri justifying the Sept 11 attacks and promising more bloodshed.