Here is a timeline of the main developments since elections in October last year, as rival Shia factions jostle for power and political deadlock leaves Iraq without a new government, prime minister or head of state.
On October 10, 2021, Iraqi holds early parliamentary elections to try to defuse youth-led protests that broke out in late 2019 over corruption and crumbling public services.
Sadr's political movement, which was already the biggest in parliament and campaigned on a nationalist, anti-corruption agenda, increases its seat tally according to preliminary results, in an vote marred by low turnout.
His rivals in the pro-Iranian Fatah alliance, representing the former paramilitary alliance Hashed al-Shaabi (Popular Mobilisation Forces), suffer sharp losses. They reject the results, calling them a "scam".
PM assassination attempt
The election outcome sparks weeks of tensions.
Hashed supporters stage a sit-in at one of the entrances to Baghdad's heavily fortified Green Zone, home to government buildings and foreign embassies.
On November 5, one demonstrator is shot dead in clashes between security forces and several hundred supporters of pro-Iranian groups.
On the night of November 6, outgoing Prime Minister Mustafa al-Kadhemi escapes unharmed after an assassination attempt at his Green Zone residence, which is attacked by an explosives-packed drone.
No group claims responsibility for the attack.
Amid the protests, Iraq's political parties attempt to form a government.
The main Shiite parties traditionally form a coalition, irrespective of how many parliamentary seats each has won.
Instead, Sadr infuriates his Shiite rivals by insisting on trying to form a "majority government" with his movement's Sunni Muslim and Kurdish allies.
Final vote results
On November 30, the final election results confirm the Sadrists' victory, with the bloc winning 73 out of 329 parliamentary seats, compared with 17 for the Fatah alliance, down from 48 in the outgoing assembly.
Stormy first parliamentary session
On January 9, 2022, the new parliament elects Sunni Muslim speaker Mohammed al-Halbussi, in a stormy first session at which rivals harangue each other over the election result.
The parliamentary vote is boycotted by the pro-Iran Coordination Framework, which draws together the Fatah alliance and lawmakers from the party of Sadr's longtime foe, ex-prime minister Nuri al-Maliki.
No new president
Parliament holds three failed attempts to elect a new Iraqi president between February 7 and March 30.
The largely ceremonial role conventionally goes to a member of Iraq's Kurdish minority.
The president's election is usually the first step in the formation of a new administration, before the designation of a prime minister and the creation of a new government.
Pro-Sadr MPs resign
On June 10, all 73 pro-Sadr MPs resign in order to pressure their rivals to fast-track the formation of a government.
Their seats go to the candidates who arrived in second place.
On June 23, 64 new MPs are sworn in, making the pro-Iran bloc the biggest in parliament.
On July 25, the Coordination Framework nominates former minister Mohammed Shia al-Sudani, 52, for prime minister.
Storming of parliament
Outraged by Sudani's nomination, Sadr supporters breach the Green Zone on July 27 and stage a brief sit-in in parliament.
Three days later, they return in their thousands and again breach the Green Zone and storm parliament, this time vowing to stay "until further notice".
They later move their protest to outside the building.
On August 12, supporters of the Coordination Framework begin their own sit-in near the Green Zone, calling for the swift formation of a new government.
Sadr bows out
On August 17, Sadr boycotts crisis talks called by the caretaker prime minister.
Ten days later, he proposes "all parties" including his own should give up government positions in order to help resolve the crisis.
On Monday, he announces on Twitter his "definitive retirement" from politics, adding that "all the institutions" linked to his Sadrist movement will be closed.