Campaign posters for upcoming early parliamentary elections are displayed in central Baghdad, Iraq, Wednesday, Sept. 29, 2021. (AP Photo)
The statement from Grand Ayatollah Ali Sistani's office came against the backdrop of potentially high rates of abstention in the October 10 ballot, which follows a popular uprising.
Initially expected in 2022, the vote was brought forward in a rare official concession to autumn 2019 protests, when tens of thousands of Iraqis took to the streets to demonstrate against crumbling public services and a government they decried as corrupt and inept.
Hundreds died in months of protest-related violence.
But the ballot has generated little enthusiasm among Iraq's 25 million voters, while the activists and parties behind the uprising have largely decided to boycott the ballot.
"The supreme religious leader encourages everyone to participate consciously and responsibly in the next elections," the statement from Sistani's office said.
Even if the process has shortcomings, "it is the best way to move the country toward a future that one hopes will be better."
One of Shia Islam's top clerics, Sistani spent years under house arrest during Saddam Hussein's repressive regime. After Saddam's fall in 2003, Sistani threw his support behind elections, was a voice for moderation, and criticised government graft.
In his statement on Wednesday, he asked voters to "benefit from this opportunity to carry out real change in the administration of the state and dismiss the corrupt and incompetent hands from its main cogs".
The statement emphasised that Sistani does not support any candidate and appealed to voters to choose those "who support the sovereignty of Iraq, its security and prosperity."
Political scientist Marsin Alshamary said that in Iraq's last elections, held in 2018, Sistani had said people could choose to vote or not.
"It was up to them. And people interpreted that as you can boycott," Alshamary said.
The 2018 elections saw the entry into parliament for the first time of candidates from the Hashed al-Shaabi, a network of mostly pro-Iran paramilitary groups who helped defeat the Sunni-extremist Islamic State group.
The Hashed held the second-largest bloc in Iraq's outgoing parliament and hopes for bigger gains this election.
Analysts are doubtful, however, favouring the movement of firebrand Shia Muslim cleric Moqtada Sadr, whose Saeroon bloc held 54 seats, the largest in parliament.