Mohsen Safaie Farahani, also a former deputy economy minister and a former MP, was one of many leading pro-reform figures detained after Iran's disputed presidential election in June, which plunged the Islamic Republic into turmoil.
Several other leading opposition supporters have earlier received jail terms on charges including acting against national security and spreading propaganda against the Islamic system.
"The court has sentenced my client to six years of compulsory jail," the semi-official Fars News Agency quoted his lawyer Houshang Pourbabie as saying, giving no further details. Under Iranian law, he has 20 days to appeal the sentence.
Last year's election sparked Iran's biggest unrest since the 1979 Islamic revolution. The opposition says the vote was rigged to secure hardline President Mahmoud Ahmadinejad's re-election.
The authorities have denied the charge of vote fraud and portrayed the huge opposition protests that followed the poll as a foreign-backed bid to undermine Iran's clerical leadership.
Thousands of people protesting against the conduct of the vote were arrested. Most of them have since been released, though more than 80 people have received jail sentences of up to 15 years and five people have been sentenced to death.
In November and December, two other leading reformers, former government spokesman Abdullah Ramezanzadeh and former vice president Mohammad Ali Abtahi, also received six-year jail terms.
Ramezanzadeh, Abtahi and Safaie Farahani held their government posts under the 1997-2005 presidency of Mohammad Khatami, who backed defeated candidate Mirhossein Mousavi in the June election.
Safaie Farahani, who also backed Mousavi's campaign, was football federation head in 1998-2002.
Separately on Sunday, the opposition Jaras website said two members of the banned Freedom Movement, Solmaze Ali Moraddi and Farid Taheri, had been detained. The party is led by former foreign minister Ebrahim Yazdi, who was detained last month.
Majid Dorri, a pro-reform student activist, was sentenced to 11 years in jail on Sunday accused of having relations with the People's Mujahideen Organisation of Iran (PMOI) and of acting against national security by participating in illegal gatherings, Jaras said.
The PMOI is an exile group opposed to Iran's Islamic system of government.
(Reporting by Hashem Kalantari; Writing by Fredrik Dahl; Editing by Jon Hemming)
