In a statement published by state media on Monday, Mr Qalibaf wrote that he was withdrawing his candidacy in an attempt to put an end to President Rouhani's "inefficient and impotent" administration.
The coalition between the two conservative nominees will benefit the country's economy in a post-election era, if Raeisi manages to assume power through the election.
The six candidates competing in Iran's presidential election have squared off in their third and final televised debate, with President Hassan Rouhani lashing out at his hardline opponents and vowing to get rid of the remaining sanctions following 2015's nuclear deal.
This time around, establishment conservative hardliners who want to unseat Rouhani are mainly placing their trust in Ebrahim Raisi, a jurist and Shiite cleric who studied at the feet of Supreme Leader Ayatollah Ali Khamenei.
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Rouhani was first elected in a landslide four years ago on a promise to reduce Iran's global isolation.
Qalibaf's decision brings the number of candidates competing in Friday's election to five, though more may drop out in the coming days to solidify support for other candidates.
"Qalibaf speaks more to the Iranian Revolutionary Guards and security apparatus, Raisi more to the traditional conservative" and clerical class, so he'll need to reach out to a wider conservative base, she said. It was Khamenei who previous year appointed Raisi, 56, to manage the Astan Quds Razavi, an Islamic charity that controls assets worth billions of dollars, as well as the Imam Reza shrine in the northeastern holy city of Mashhad.
Conservatives accuse Rouhani of succumbing to Western pressure and for compromising Iran's sovereignty.
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In the ongoing presidential campaign, Rouhani said he would focus on tackling unemployment and stimulate production.
Iran's 12th presidential election candidate, Mohammad Baqer Qalibaf (2nd L), attends a gathering of his supporters in the northern Iranian city of Rasht, May 15, 2017. He called a vote for Raisi a "crucial decision" to "preserve the unity" of the revolution.
He added that the development movement in Iran started with the reformist Govt of former President Mohammad Khatami and continued with the current Govt of President Hassan Rouhani.
Raisi has pledged to support the poor with a monthly cash payment equivalent to $65 - about a sixth of what a menial laborer makes in a month. Both snubbed Rouhani, who himself is a cleric.
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It comes just as Turkey sent a high powered delegation to Washington to explain to the Americans Ankara's misgivings in detail. The YPG militia says the decision is "historic" and a "sign of confidence" in the group, in a statement released Wednesday.
"The same people who promised that the nuclear deal would enable Congress to push back against Iran-literally the very same people-are now mobilizing to prevent any pressure against Iran over its threats to us and our allies", the adviser told TWS. "In Tehran, his votes will go mainly to Rouhani but outside Tehran his supporters will vote for Raisi".