The announcement has raised fears that Sadr's supporters might escalate their protests, fuelling a new phase of instability in Iraq.
Iraq's Shia Muslim cleric Muqtada al Sadr has announced that he is quitting politics and closing his institutions in response to an intractable political deadlock.
"I hereby announce my final withdrawal," Sadr said in a statement posted on Twitter on Monday.
He criticised fellow Shia political leaders for failing to heed his calls for reform. He did not elaborate on the closure of his offices, but said that some of his cultural and religious institutions would remain open.
Sadr withdrew his lawmakers from parliament in June after he failed to form a government of his choosing.
A political impasse between him and Shia rivals close to Iran has given Iraq its longest run without a government.
Supporters of Sadr have since the end of July occupied parliament and protested near government buildings, halting the process to choose a new president and prime minister.
Fears of more protests
Monday's announcement raised fears that Sadr's supporters might escalate their protests, fuelling a new phase of instability in Iraq.
The standoff in Iraq is the longest stretch without a fully functioning government in the nearly two decades since Saddam Hussein was overthrown in a US-led invasion in 2003.
Sadr has called for early elections and unspecified changes to the constitution after withdrawing his lawmakers from parliament in June.
The country has struggled to recover since the defeat of Daesh in 2017 because political parties have squabbled over power and the vast oil wealth possessed by Iraq, OPEC's second-largest producer.