Texas-born Ali signed confessions and made statements admitting to the plot after being picked up in Saudi Arabia where he was studying in 2003.
He also admitted to being part of an Al Qaida cell.But his attorneys claimed at trial he had been tortured into confessing by the Saudi police.
However the U.S. appeals court Tuesday upheld a life imprisonment sentence and rejected arguments by attorneys that it was unreasonable and violated various constitutional provisions.
Abu Ali initially was sentenced to 30 years in prison, but the appeals court in 2008 sided with U.S. Justice Department prosecutors and sent the case back for resentencing.
He then received the maximum term of life in prison.
The U.S. Attorney for the Eastern District of Virginia Neil MacBride said he was pleased the appeals court upheld the sentence for a man who conspired to assassinate Bush and other high-ranking U.S. government and military leaders.