Senior Iranian reformist figure Mostafa Tajzadeh submitted his candidacy Friday for June's presidential election.
Tajzadeh, 64, has campaigned for years for democratic and "structural changes" in the country.
After submitting his candidacy at the interior ministry, Tajzadeh, who served as deputy interior minister during the 1997-2005 tenure of reformist former president Mohammad Khatami, told reporters he was a "citizen, reformer" and "political prisoner for seven years".
He also condemned "discrimination", "internet blocking", "the military's interference in politics, the economy and elections", "costly foreign policy, anti-Americanism and pro-Russian (diplomacy)" in Iran.
His candidacy could face obstacles due to a prison sentence served after he was jailed in 2009 and convicted the next year on charges of harming national security and propaganda against the regime.
Thousands of people were detained during demonstrations against the disputed 2009 re-election of hardline president Mahmoud Ahmadinejad, contested by an opposition backing unsuccessful reformist candidates Mehdi Karoubi and Mir Hossein Mousavi.
Since his release in 2016, Tajzadeh has called often on authorities to free Mousavi and Karoubi, who have been under house arrest for a decade over the protests.
Accompanied by his wife, Fakhrossadat Mohtashamipour, also a reformist activist, Tajzadeh spoke up Friday for women's rights in Iran.
"I am opposed to laws that discriminate against women," he said, adding that he was against "compulsory veiling" but not against veiling per se.
"We will stay the course of dialogue and reconciliation, even if the other side intends to go to war with us," he added, implicitly rejecting attacks by some ultra-conservatives.
Earlier on Friday, an ultra-conservative lawmaker and former head of the Atomic Energy Organization of Iran (AEOI), Fereydoun Abbasi Davani, also registered his candidacy.
The 62-year-old nuclear physicist, who in 2010 escaped an attempt on his life attributed by Iran to Israel, rejects any "compromise" with the West and is a resolute opponent of the embattled 2015 international accord on Iran´s nuclear program.
The deal, which Tehran and other parties are attempting to salvage, is defended by its main architect on the Iranian side, outgoing President Hassan Rouhani, who is constitutionally barred from running for a third consecutive term.
Ahmadinejad has also put his name forward as a candidate for the June 18 election.
