Mr Obama had pledged in January 2009 to close the prison within a year US President Barack Obama is lifting the two-year freeze on new military trials for detainees at the Guantanamo Bay prison.
Mr Obama also announced a new process for continuing to hold those detainees not charged or convicted but deemed too dangerous to free.
He said the measures would “broaden our ability to bring terrorists to justice”.
Mr Obama had pledged in January 2009 to close the prison within a year.
“The American system of justice is a key part of our arsenal in the war against al-Qaeda and its affiliates,” Mr Obama said in a statement.
He added that military commissions “ensure that our security and our values are strengthened”.
US defence secretary Robert Gates issued an order on Monday revoking his previous suspension on the “swearing and referring of new charges in the military commissions”.
New military commissions at the prison, which holds a number of top suspects from the 9/11 attacks and other strikes against the US, have been suspended since January 2009.
Mr Obama ruled in an executive order that detainees would have the right to a periodic review of the reasons for their detainment.
The order was designed to ensure inmates detained indefinitely without trial were only kept in prison when it was lawful and necessary to do so, the White House said.
“I am announcing several steps that broaden our ability to bring terrorists to justice, provide oversight for our actions and ensure the humane treatment of detainees,” Mr Obama said.
The president also reserved the right to try some suspects from Guantanamo Bay prison in federal prisons on the US mainland, a move that has been repeatedly blocked by members of Congress.
The White House said it would allow certain trials to resume, having carried out key reforms such as a ban on the use of statements taken under “cruel, inhuman or degrading treatment” and a better system for handling classified information.
“With these and other reforms, military commissions, along with prosecutions of suspected terrorists in civilian courts, are an available and important tool in combating international terrorists,” the Obama administration said.
The announcement on Monday is being seen as the president’s latest attempt to work around “war on terror” policies put in place by the previous Bush administration.
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