BBC News, Tehran
Iran's main reformist candidate, initially barred from standing in next month's presidential election, has now said he will contest the poll.
Moin says his decision to run was a difficult one to make
Mostafa Moin was among 1,000 candidates disqualified from running.
But a last-minute intervention by Iran's supreme leader, Ayatollah Khamenei, allowed him to stand.
Some reformists had urged Mr Moin to boycott the polls in protest, but he said he had decided to run "to defend the rights of the silent majority".
The former education minister said it had been a difficult choice to make, following his "illegal and unreasonable disqualification".
The initial decision to bar him from standing sparked calls for a boycott from students.
Balance of power
Although the reformists swept the last two presidential elections, they are unlikely to win this time.
They failed to deliver on their promises while in office because the post of president simply is not powerful enough to take on the hardliners who control the judiciary, security forces and now the parliament as well.
The latest opinion polls put former President Ali Akbar Hashemi Rafsanjani in the lead but so far without the necessary 50% of the votes to clear the first round of elections.
Mr Rafsanjani, who says he is against extremism, has been trying to dispel the widely held belief that he is one of Iran's richest men.
He says he has spent all the money he had as a student and does not even own a house or land in the capital now.