Rezaian, the US newspaper's Tehran correspondent, was arrested in July 2014, accused of spying and tried in four hearings behind closed doors, the last of which was in August.
"The verdict for this case has been issued," Gholamhossein Mohseni Ejeie, who as well as being the judiciary's spokesman is its deputy chief, was quoted as saying on its official website.
"This verdict can be appealed. The time for an appeal is not yet over. So the court waits and if it doesn't receive an appeal... The verdict becomes final."
The treatment and trial of the journalist -- a dual Iranian-American citizen -- has drawn condemnation from his family, employer and press freedom groups.
The Post has called the trial a "sick brew of farce and tragedy" and said it "has been anything but transparent and just".