Early results from Iraq's electoral commission place al-Sadr and Prime Minister Haider al-Abadi as the two leading politicians in the race - the fourth election since the US invasion in 2003 brought down Saddam Hussein's dictatorship, and the first after Iraq's three-year war against ISIS, which ended last December. While Sadr is unlikely to totally disavow any of Iraq's allies, both the United States and Iran will be sad to see more easily controlled leaders replaced with more independent ones, and that could have a long-term drag on relations.
Seats in parliament will be allocated proportionately to coalitions once all votes are counted. Prime Minister Hayder Abadi's faction may be a possibility, as Sadr has said it's possible they could form a government together.
While sectarianism may have dominated the Iraqi landscape in the past, the focus of most disenchanted Iraqis is on tackling widespread corruption, a faltering economy and the mammoth reconstruction effort after Daesh. Al-Sadr commanded fighters in the war against the IS group and headed a powerful militia that fought US forces in Iraq prior to 2011, but his 2018 campaign focused on social issues and eliminating government corruption.
With the electoral law amendments in 2010, the onus is not on the bloc with the largest number of votes to form a government, but on the formation of the largest coalition alliances.
Saturday's vote was the first parliamentary election since ISIS took over large parts of the country in 2014.
Turnout was 44.52 percent with 92 percent of votes counted, the Independent High Electoral Commission said - that was significantly lower than in previous elections.
Whoever wins the most seats still must negotiate a coalition government, which must be formed within 90 days of the results being formally announced. The other winning blocs would have to agree on the nomination.More news: Alonso urges McLaren to kick on after season's best qualifying
"We support a fair and transparent process", he said.
"This vote is a clear message that the people want to change the system of governance that has produced corruption and weakened state institutions", said Fahmy.
Abadi - who came to power as ISIS swept across Iraq in 2014 - has been a consensus figure who balanced off the USA and Iran.
The winners not only scramble the pyramid of power in Iraq but also raise the possibility of a government with radically new priorities. Authorities are seeking as much as $88 billion for postwar reconstruction.
Celebrations erupted in Baghdad's Sadr City, an impoverished quarter that is home to about 3 million people and is named after the cleric's father, Ayatollah Mohammed Sadeq al-Sadr, who was killed by suspected agents of Saddam Hussein in 1999.
After the announcement that the Marching Towards Reform was ahead in Baghdad, supporters took the streets in the capital to celebrate a win.
Tensions in the region have mounted - and in particular between the United States and Iran - partly because of President Trump's decision last week to withdraw the United States from the nuclear deal with Tehran. That they were able to express themselves democratically is even more encouraging. If parliament does grant him a second term, Abadi will remain under pressure to maintain the balancing act between Washington and Tehran.