Ganji (right) cannot appeal against the sentence
Ganji, a supporter of the reform movement in Iran, was convicted of damaging state security by attending a conference in Berlin on the future of Iran.
BBC Iran analyst Sadeq Sabeh says the sentence is a blow to President Mohammed Khatami, who has promised more openness and the rule of law.
In May, the 10-year sentence, followed by five years' internal exile, was reduced on appeal to six months in jail.
But despite the appeal Ganji remained in prison facing other charges.
Prosecutors then took the case to a higher court, which imposed a harsher penalty.
A court statement said that the ruling was definitive and therefore not subject to further appeal.
Clampdown
Our correspondent says Ganji made enemies by naming members of the conservative establishment as being responsible for the killing of dissidents and intellectuals.
Since the election in 1997 of reformist President Khatami, around 40 mostly pro-reform newspapers have been shut down.
Dozens of Mr Khatami's supporters have been jailed or remanded in custody on subversion charges.
A number were convicted as a result of their attending the Berlin conference last year, which was branded as anti-Iranian after being disrupted by émigré groups.
And despite the president's landslide re-election last month, a French-based press defence group said that the plight of journalists was worsening in Iran.
A statement by Reporters sans Frontieres described Iran as "the largest prison for journalists in the world", adding that of 27 journalists known to be in jail, 21 were being held in unknown locations.
Ganji has been in prison for the last fifteen months and he has accused prison authorities of torturing him.
He has been on hunger strike several times to protest at his detention in solitary confinement in a Tehran prison.