Al-Sadr's Marching Towards Reform alliance, which includes the Iraqi Communist Party, won 54 seats in Iraq’s 329 seat parliament.
The turnout was only just over 45 percent and it took over a week for the results to be published.
When they came out over the weekend, the reactions were mixed.
“These elections are not satisfactory and not correct,” says Baghdad-based businessman Louis Climis, contacted by phone by RFI.
“Because there were many instances of falsification and there was intervention by political blocs and exterior parties also.
“I’m not optimistic. Certainly I don’t see that the regime changes politics, but I see there is the same status, the same corrupt persons which control politics.”
Will the election outcome strengthen Shia-led Iran's influence in its neighbour?
Not according to most analysts, who tend to agree that Tehran may have lost a pawn here.
Although al-Sadr did receive Iranian funding when he was leading an uprising against US troops back in 2004, his campaign line was that he does not want the Iranians to run the show in Baghdad.
US backed ex-PM
But the US, which might have expected to have a solid foothold in the country when it ousted Saddam Hussein in 2003, did not get the result they wanted, either.
"They are not happy but I think they are probably making a mistake again,” says Patrick Cockburn, author of several books on this part of the Middle East, including studies on the Islamic State armed group, and staff writer for the British newspaper the Independent.
“They put great effort into securing the highest possible vote for the current prime minister, Haider Al-Abadi, and obviously that didn’t work out the way they wanted it."
As an Iraqi nationalist, al-Sadr is anti-Iranian as well as anti-American, he points out. "But they don’t look at it that way. They want somebody who is pro-American.”
Any Iraqi leader is going to have to balance between Washington and Tehran to some degree “to cultivate good relations with both and bounce them against each other”, he says.
Israel worried about US losing hold
There were mixed reactions in Israel, too.
“Diminishing the Iranian influence in Bagdad is beneficial to Israel,” says Israeli academic Eytan Gilboa. ”Because it would disrupt the strategic design of Iran to build the Shiite crescent, from Tehran, Bagdad, Damascus and Beirut.
“But if the US is also kicked out of Iraq, then this is a negative development from the Israeli perspective.”
Al-Sadr faces an immense task.
His campaign involved a coalition with Iraqi left-wing parties and he won votes because of his anti-sectarian, anti-Iran and anti-American stand.
But 54 seats does not give him an absolute majority.
So forming a coalition may involve joining forces with supporters of his main opponent, Abadi.
So difficult negotiations look likely for the next few weeks and months.