Sudanese-born Ibrahim al-Qosi, 50, had admitted conspiracy and providing support for terrorism.
However, he could serve far less time because of a plea deal which is likely to remain secret for several weeks.
Qosi, who was detained in Afghanistan in 2001, also admitted working as Bin Laden’s bodyguard and helping him avoid capture by US forces.
The sentence will now be reviewed by the Pentagon.
Qosi was detained by US forces after fleeing an al-Qaeda hide-out in Afghanistan’s Tora Bora mountains.
He has admitted running a kitchen in Bin Laden’s compound while being aware that al-Qaeda was a terrorist organisation.
At his sentencing hearing, military prosecutors said Qosi had insulted the tribunal’s intelligence by insisting he was a mere cook.
He is only the fourth person held at Guantanamo Bay to be convicted, and the first since President Barack Obama took office in 2009.
The centre has held more than 800 alleged militants of whom about 180 remain in custody.
Mr Obama had pledged to shut the controversial facility by January this year, but a deadlock with Congress over where to house remaining detainees delayed the plan.
Source: BBC