Voting for the 290-seat parliament 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 6,300 candidates, including 586 women, are competing for a place in the parliament, while 161 others are running for the Assembly of Experts.
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.
In their campaigns, candidates zeroed in on economic topics, including unemployment, economic growth, and recession.
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 Hassan Rouhani is seeking re-election in the Assembly of Experts, a clerical body which is tasked with monitoring the performance of and appointing the Leader.
Members of the Assembly serve eight-year terms while MPs are elected every four years.