Sadeq Mahsouli, a former Revolutionary Guards comrade of the president, takes charge of the ministry responsible for overseeing elections seven months before a presidential poll. Ahmadinejad is expected to run but has yet to declare.
Tuesday's vote in favour of Mahsouli — 138 of the 273 lawmakers present, only just more than half — will be a relief to Ahmadinejad, who has faced mounting criticism from parliament particularly over his economic policies and surging inflation.
Mahsouli had been a nominee for oil minister early in Ahmadinejad's term but withdrew after lawmakers criticised his wealth and lack of related experience. Parliament must approve ministers and can also kick them out.
The previous interior minister, Ali Kordan, was forced out by parliament for having a fake degree from Britain's Oxford University.
"Today we need someone at the Interior Ministry who can manage and put things together. After all, we have had some shakiness at the ministry in the last five to six months," the president told lawmakers in an address to win support.
Mahsouli had campaigned hard before the vote to secure the backing of lawmakers, many of whom were wary of the choice.
"Cooperation between the government and parliament is very important and, through this cooperation, we should disappoint our enemies," Ahmadinejad said in a speech that some initially reluctant MPs said struck a conciliatory tone.
Some still opposed Mahsouli, saying the pick was part of Ahmadinejad's re-election campaign before the June vote.
"This choice is a choice for the election," said conservative MP Hossein Falahatpisheh, adding that Mahsouli had been a campaign manager for Ahmadinejad in past elections.
"By selecting him now as his interior minister, it is like forming an election headquarters before the election," he said.
Mahsouli denied the charge in his own speech to lawmakers. and said he would ensure a fair election process as minister.
Parliament Speaker Ali Larijani has said that, based on Iranian law, Ahmadinejad will need a vote of confidence for his whole cabinet if another cabinet post is changed.
