The 77-year-old formally stepped down last year following anti-government protests that left more than 550 dead, making him the first prime minister to resign since the US-led invasion that toppled Saddam Hussein in 2003.

But he stayed on as caretaker PM for five months as Iraq's notoriously divided political factions wrangled over a successor -- until they agreed to endorse spy chief Mustafa Kadhemi, whose government received parliament's vote of confidence early Thursday.

With his term officially cut short by more than two years, Abdel Mahdi is likely to be remembered for the deadly rallies that rocked his country, tit-for-that conflict between the US and Iran on Iraqi soil and an oil price collapse that sent the economy into free-fall.

In January, a US drone strike killed Iranian general Qasim Soleimani and Iraqi commander Abu Mahdi al-Muhandis in Baghdad, and Iran retaliated with a volley of ballistic missiles against US troops stationed in western Iraq.

Abdel Mahdi, under whom relations with Washington have been their most strained in years, could do little but appeal for calm.

When Iraq's parliament voted days later to oust all foreign troops from the country, Abdel Mehdi pledged to honour their decision but did not ultimately implement it.

"He is someone who likes consensus, who is hands-off and does not like to take dramatic action," said a government source close to him.

- Ready to resign -

Abdel Mahdi was named prime minister in late October 2018 as a consensus candidate among Iraq's divided political giants and its competing international allies, Iran and the US.

He was cautiously backed by the parliamentary blocs of Hadi al-Ameri, a leading member of the Hashed al-Shaabi paramilitary force, and populist cleric Moqtadr Sadr.

He also had the support of the autonomous Kurdish government in the north and had hoped to normalise ties with them, and to balance between Iraq's competing international allies, Iran and the US.

But with no solid political base of his own, he was seen as the weakest prime minister in Iraq's history.

In taking the post, Abdel Mahdi admitted it was a "heavy responsibility" and that he was keeping his resignation letter "in his pocket".

His tenure began optimistically -- with the re-opening of the Green Zone, trips abroad to rebuild Iraq's diplomatic standing and new committees pledging to fight corruption and rebuild the country after a three-year fight against the Islamic State jihadist group.

- 'Fighting off a coup' -

But few foresaw that Abdel Mahdi would be felled by protests that brought tens of thousands into the streets from October, the largest grassroots movement in Iraq's history.

As the death toll mounted, government sources told AFP the premier became increasingly "conspiratorial."

"He was convinced he was fighting off a coup," the government source said.

The turning point was three days of violence in his birthplace of Nasiriyah in late November, after which the country's top Shiite cleric urged parliament to withdraw support.

Political parties launched talks to find a replacement but two men appointed PM-designates failed to get their cabinet line-ups to a vote.

In the meantime, Abdel Mahdi managed day-to-day affairs, and government sources said Iran would have liked to see him serve out the rest of his term.

But that was seen as an untenable choice by those who blamed him for protest-related violence and by the US.

- A long career -

With a burly physique and a face framed by spectacles and a thin moustache, he is a fluent French speaker and also has an excellent command of English.

A Shiite raised in Baghdad, Abdel Mahdi was born to the son of a minister during Iraq's monarchy, which met a bloody end in 1958.

He joined the Baath party, which brought Saddam to power in the late 1970s, before switching to oppose the dictator, first as a communist and then as an Islamist member of the Supreme Iraqi Islamic Council, a Shiite movement close to Iran.

He served as a member of the interim council installed by the US military, then finance minister, vice president and finally, oil minister under Haider al-Abadi, the man he was to succeed as premier.

"This is someone who has at various points in his career been a communist, an Islamist, an independent," said a former official who has known him for years.

"What does that tell you about what he wants? Power."