Jalili, 58, will aim to unify Iran's fragmented conservative factions in the bid for the presidency when he faces Masoud Pezeshkian next Friday.
A relatively reserved figure with a well-groomed white beard and spectacles, Jalili will seek to persuade voters he is best suited to lead Iran under the guidance of supreme leader Ayatollah Ali Khamenei, who holds ultimate authority in the country.
In the first round, Jalili secured more than 9.4 million votes, buoyed by a substantial base of hardline supporters who embrace the slogan "no compromise, no surrender" to the West.
Born on September 6, 1965, in the northeastern city of Mashhad, Jalili comes from a devout middle-class family.
Soft-spoken, but with a rigid, religious persona, he has held several senior roles throughout his career.
He is currently one of Khamenei's representatives in the Supreme National Security Council, Iran's top security body.
Jalili fought in the 1980-88 Iran-Iraq war and was hit by shrapnel on the front lines, resulting in the amputation of his right foot.
From 2007 to 2013, he led negotiations on Iran's nuclear programme, consistently sticking to an uncompromising stance.
Critics accused him of making ideological statements during negotiations with Western governments, rather than clearly articulating Iran's position.
He has staunchly opposed the 2015 nuclear deal with the United States and other world powers, arguing it violated Iran's "red lines" by accepting inspections of nuclear sites. The deal collapsed in 2018.
Jalili holds a doctorate in political science from Emam Sadegh University in Tehran, an institution established to train the cadres of the Islamic republic.
In the early 2000s, he was part of the supreme leader's office, responsible for providing key reports on major strategies.
Under hardline populist president Mahmoud Ahmadinejad, Jalili served as deputy foreign minister for Europe and South America.
In the 2013 presidential race, Jalili finished third, securing only 11 percent of the vote.
In 2021, he withdrew his candidacy in favour of ultraconservative Ebrahim Raisi, who went on to win. Raisi's death in a helicopter crash last month triggered the snap election.
