A three-judge panel of the 4th U.S. Circuit Court of Appeals unanimously rejected Moussaoui's claim that he was denied potentially helpful evidence during his trial and was restricted in choosing his own counsel.
He is serving life in prison after pleading guilty to helping plan the attacks.
Moussaoui's appeal said his right to choose his counsel was violated because the judge required that any attorney involved in his defense undergo a national security background check.
The appeal contended that it is unconstitutional to require government approval of a defendant's hired or pro bono counsel.
The appeal also argued that Moussaoui's rights were violated because his attorneys could not talk to him about potentially helpful evidence gleaned from classified material.
During arguments in the appeal last September, his lawyer argued that because of the problems with evidence and counsel, Moussaoui's guilty plea was invalid.
A federal prosecutor countered that Moussaoui got exactly what he wanted when he ignored his attorneys' advice and pleaded guilty before the evidence he had sought could be provided.