The Pentagon said that after the attacks in Tanzania and Kenya, in which more than 200 people died, Ghailani worked as a bodyguard for Osama bin Laden, the al-Qaeda leader, forged documents and trained recruits.
Ghailani also hid in the South Waziristan tribal region of Pakistan on the border with Afghanistan, but was driven out by a major military operation, Pakistani security sources said.
He is accused of playing a key role in the Tanzanian bombing, including buying explosives and detonators and moving bomb parts to safe houses around Tanzania's biggest city, Dar es Salaam.
Prosecutors also allege he scouted the US embassy with the driver of the vehicle that carried the bomb.
Six other al-Qaeda suspects are facing death penalty charges at the Guantanamo Bay hearings, including Khalid Sheikh Mohammed, who allegedly planned the September 11, 2001 attacks on the US, which killed nearly 3,000 people.
A total of 15 Guantanamo detainees have now been charged under the 2006 Military Commissions Act which set up the tribunals.
Human Rights groups have condemned the tribunals, which were set up to try "enemy combatants" held by the US at Guantanamo, as being weighted in favour of obtaining "war on terror" convictions.
They also say the trials will not be credible.
"These commissions aren't fit to try anybody, still less to
condemn anybody to death," Jumana Musa, an Amnesty International USA lawyer, said.
Concerns have also been raised about the use of harsh interrogation techniques, including waterboarding - which simulates drowning - on suspects at Guantanamo bay.
"It's a particular concern that he could be sentenced to death under a system that allows, in certain circumstances, the use of evidence obtained through highly abusive interrogations, and [that] lacks established rules and procedures," Jennifer Daskal of Human Rights Watch said.