He was arrested by Afghan fighters in 2001, and turned over to a US army officer who testified that Hamdan had two surface-to-air missiles in his car.
After two days of testimony, the judge, Captain Keith Allred, rejected the claim that Hamdan was a prisoner of war.
He said there was enough evidence to suggest that he was an "alien unlawful enemy combatant".
That unlawful distinction means Hamdan cannot benefit from prisoner of war protections defined by the Geneva Conventions.
|Hamdan was captured in Afghanistan with |
two surface-to-air missiles [AFP]
Hamdan, who is 37 according to US military records, faces up to life in prison if the tribunal convicts him of conspiracy and supporting terrorism.
Allred said there was credible evidence that the Yemeni prisoner was bin Laden's personal driver and occasional bodyguard from 1997-2001 and sometimes picked up and delivered weapons.
Hamdan's military lawyer, Lieutenant Brian Mizer, said he was disappointed and may make the ruling part of an eventual appeal if Hamdan is convicted.
"I think the evidence was that he was a prisoner of war," Mizer said.
"He was caught taking conventional weapons to a conventional force and ... it's not a crime to be a soldier.''
The ruling is a victory for the Pentagon, which has struggled to prosecute Guantanamo detainees amid repeated legal challenges.
The decision clears the way for a trial that could start by March next year in what would be the first US military tribunal since the World War II era.
|No one has yet been tried at Guantanamo, |
where about 290 detainees remain [EPA]
Brigadier-General Thomas Hartmann, the legal adviser to the military tribunal system, said the ruling was "a sign that we will move forward".
To underscore that point, Hartmann noted that the military prepared charges on Thursday against Ahmed Mohammed Ahmed Haza al-Darbi, a Saudi prisoner at Guantanamo accused of helping to organise an al-Qaeda plot to attack a ship in the Strait of Hormuz or off Yemen.
The US Supreme Court is deliberating its third case on Guantanamo detainees, the outcome of which could reverse Thursday's decision on Hamdan.