Aref, the only reformist candidate still standing in the election, said on Tuesday morning that he had received a message from ex-president Mohammad Khatami advising him to quit the race.
"At dusk on Monday... I received a letter from Mohammad Khatami... he said it would not be wise for me to remain in the race," Aref wrote in a withdrawal statement that was published on his website. Khatami remains an influential figure in Iran's reformist wing.
"In consideration of Mr. Khatami's explicit opinion, and the experiences of two past presidential elections, I declare my withdrawal from the election campaign," Aref said.
The withdrawal is the second in two days after ex-parliamentary speaker and conservative Gholam Ali Haddad Adel - who had not been considered a front-runner - pulled out of the race.
Centrist Rowhani still in running
Aref's decision has already been interpreted as a move to support centrist candidate Hasan Rowhani, who advocates a more moderate path to reform. While Aref's statement did not mention Rowhani, he has stated his support for an electoral alliance in the past. The AFP news agency reported on Tuesday that Khatami's advisory council had given their backing to Rowhani as the "reformist camp candidate."
Rowhani was the main nuclear negotiator for Iran in Khatami's administration and served as a top security official under former president Akbar Hashemi Rafsanjani.
The presidential vote, set for June 14, is Iran's first since 2009, when the re-election of President Mahmoud Ahmadinejad sparked months of popular protests after allegations that the poll had been rigged.
rc/ipj (AFP, AP, dpa, Reuters)