But can he really sideline powerful foreign players and domestic rivals to take control?
The movement has pitched itself as a challenge to Iraq's entrenched elite and ridden popular protests over graft to drum up support.
However, with months of wrangling expected ahead, it remains far from certain that he will get the chance to realise his ambitions. Corruption has been at the top of Sadr's agenda for several years.
A source familiar with ongoing talks between Iraqi political parties told Kurdistan 24 on Tuesday that the head of the Quds Force of Iran's Islamic Revolutionary Guard Corps Qassem Soleimani is now in Baghdad to meet with Shia parties in an attempt to prevent Sadr from choosing the new Premier.
In a sign that he is angling to chart a different course, he visited regional Sunni powerhouse Saudi Arabia previous year, as Tehran's rival seeks to play a greater role in Iraq. The government should be formed within 90 days of the official results.
Influential Shia cleric Muqtada al-Sadr on Monday revealed potential political allies needed to form a new government following Saturday's as-of-yet inconclusive elections.
The surprising upset in elections this weekend by Mr. Sadr's unlikely alliance of communists, Sunni businessmen and pious community activists comes amid long-simmering anger at the established politicians who have controlled government since Iraq's first democratic election in 2005 after the fall of dictator Saddam Hussein. The group overran a third of Iraq in 2014.
Sadr will not become prime minister, as he wasn't on the ballot, but a victory would allow him to appoint someone to the post.
Suleimani has reportedly called for a union between Abadi's bloc, the Conquest Alliance of former anti-Daesh commander Ameri and former premier Nouri al-Maliki.