Reformist Mohsen Mehralizadeh, hardliner Alireza Zakani and conservative Saeed Jalili dropped out of Iran's presidential race.
Mr Mehralizadeh was the only reformist candidate in the upcoming election. He gave his resignation letter to the Interior Ministry, state-run news agency Irna said.
Mr Mehralizadeh previously served as governor in two Iranian provinces. He was also the vice president in charge of physical education under reformist president Mohammad Khatami and a deputy in the Atomic Energy Organisation of Iran. He ran in the 2005 election, coming last.
Mr Zakani, the most conservative of the candidates, said he would support front-runner Ebrahim Raisi, also a hardliner. "I believe him to be qualified and will vote for him, and I hope that fundamental reforms take place in the country with him being elected," Mr Zakani said
A former veteran of the Iran-Iraq war and a commander of the Islamic Revolutionary Guard Corps' affiliated volunteer Basij militia, he was disqualified in 2013 and 2017 from running for president. Mr Raisi said of Zakani: "I sincerely thank my dear brother, Dr Alireza Zakani, who decided to run in the election based on his revolutionary duty ... today he decided responsibly."
Mr Jalili, earlier the top nuclear negotiator for former hardline President Mahmoud Ahmadinejad, endorsed hardliner and front runner Mr Raisi.
With the election just days away, Mr Mehralizadeh Mr Zakani and Mr Jalili’s decision to drop out of the race is seen as an effort to boost the chances of candidates like Mr Raisi and former Central Bank chief Abdolnasser Hemmati.
Mr Hemmati, formerly a member of the Rouhani administration, is running as a moderate. The latest Ispa poll shows Mr Hemmati trailing Mr Raisi.
Mr Raisi is expected to win the election largely because of the historically low voter turnout, which often favours hardline candidates.
On Monday a poll by the Iranian Students' Polling Agency, found just 42 per cent of about 5,000 respondents planned to vote. Sixty per cent of those voting said they would back ultra-conservative cleric and Iran's judiciary chief Mr Raisi.
Over the next 24 hours, candidates will do their final canvassing before a campaign blackout is imposed, which could include more candidates dropping out. Last-minute withdrawals by candidates are not uncommon in Iran.