Voting for the 290-seat Parliament (Majlis) and the 88-member Assembly of Experts will be held simultaneously. Some 55 million Iranians are eligible to vote in the two elections.
As many as 4,844 candidates, including about 500 women, are competing for a place in the Parliament, head of the Interior Ministry's election headquarters Mohammad Hossein Moqimi said on Thursday.
The week-long campaigns of the candidates officially ended at 8 a.m. local time (0430 GMT) on Thursday, 24 hours before the beginning of the votes.
Polls will open at 0430 GMT and are scheduled to close at 1430 GMT but voting could be extended if required.
On Wednesday, Interior Minister Abdolreza Rahmani Fazli said some of the candidates had pulled out.
"It now leaves around 17 people competing for each parliamentary seat," he said.
Ahead of the voting, Leader of the Islamic Revolution Ayatollah Seyyed Ali Khamenei warned against enemy plots to infiltrate the elections, calling on the nation to remain vigilant.
“The nation neither wants a pro-government parliament nor an anti-government one,” Ayatollah Khamenei said, PRESS TV reports.
"They want a courageous and devout parliament that knows its duties and is not intimidated by the United States," the Leader added.
Iran’s President Hassan Rouhani texted mobile phone users urging them to vote, saying participation was needed "to build the future of the country with plenty of hope."
What are the stakes?
In their campaigns, candidates zeroed in on economic topics, including unemployment, economic growth, and recession. The official unemployment rate stands at 10 percent and inflation hovers around 15 percent.
Members of Parliament generally break into two main blocs, those who support a reformist agenda and those who call themselves principlists.
Reformists are vying for seats under the leadership of Mohammed Reza Aref, a former vice president, while the main principlist faction in the elections is headed by Gholamali Hadad Adel, a former parliament speaker.
Any new legislation must pass through the Parliament; hence, the elections matter to the president to press ahead with his plans.
President Rouhani is fresh from a landmark nuclear agreement which he hopes to use to bring economy out of a nagging stagflation. He managed to pull enough support from the Parliament to push forward the nuclear deal.
Rouhani led a delegation of 120 key traders and officials to Europe, culminating in the signing of a series of business deals worth about $40 billion.
The impact of the deal, however, has yet to be felt on the streets. Moreover, critics of the government are worried.
"We are worried about the numerous (Western) companies that are constantly travelling to Iran since the nuclear agreement,” Hadad Adel said on Wednesday.
"This country should not turn into a market for the consumer goods of alien forces.”
Assembly of Experts
President Rouhani is also seeking re-election in the Assembly of Experts, a clerical body which is tasked with monitoring the performance of and appointing the Leader.
As many as 161 others are running for the Assembly of Experts. Members of the Assembly serve eight-year terms while MPs are elected every four years.