A reformist and an ultraconservative will square off in a runoff election Friday as neither candidate garnered the majority of votes required to win the presidency in a first round plagued by record low voter turnout and dissatisfaction with the political establishment.

The July 5 election, being held a year early because of the death of former President Ebrahim Raisi in a May helicopter crash, will decide whether the reform candidate, Dr. Masoud Pezeshkian, or the hard-liner Saeed Jalili, will assume the presidency of a country beleaguered by a crippled economy, internal protests and foreign policy challenges.

In the first round, 60 percent of eligible voters either did not show up at the polls or cast a blank vote, in protest of the ruling establishment, which they view as inefficient and incapable of solving Iran’s domestic and international problems.

Dr. Pezeshkian received over 10.4 million votes (42.4 percent) of the approximately 24 million cast, and Saeed Jalili received 9.47 million (38.6 percent).

While Dr. Pezeshkian received the most votes in the first round, it’s unclear who will emerge on top on Friday. The third-place candidate, Mohammad Baqer Ghalibaf, who received 13.8 percent of first-round votes, endorsed Mr. Jalili, but earlier polling showed that many of Mr. Ghalibaf’s supporters would not support Mr. Jalili.

Here is what to know about Dr. Pezeshkian and Mr. Jalili: