Although protests over the past year have resulted in repeated promises of reform, little in the way of concrete progress has been made, as those in a position to effect change benefit from the existing system.
Populist Shiite cleric Moqtada al-Sadr, who had called for the demonstration, made a brief appearance at the rally in Tahrir Square, which was packed with flag-waving protesters.
Protesters fought to get closer for a glimpse of the cleric but he quickly departed, and his remarks were instead read out by another speaker.
He has organised repeated protests calling for reforms, during which demonstrators have on several occasions breached Baghdad's Green Zone, a fortified area that is home to key government institutions and foreign embassies.
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Speakers led the protesters in chanting slogans including: "Yes, yes to reform," "No, no to sectarianism" and "No, no to corruption."
The rally went ahead despite a warning from the government that it could distract security forces from the war against the Islamic State group, and a statement from the Joint Operations Command terming it "unauthorised" and saying anyone who appeared with arms would be treated as a "terrorist threat."
Protesters were repeatedly searched by organisers on the way to the demonstration, and strands of barbed wire kept them away from the bridge across the Tigris River that they had previously used to reach the Green Zone.
The route to the bridge was also blocked by slabs of heavy concrete blast wall and defended by riot police.
Internet connections were cut during the demonstration, but restored later in the morning.
"These people (who) came after 2003... They failed. They failed! They didn't do anything," Daradji said, referring to politicians who came to power after the 2003 overthrow of dictator Saddam Hussein.
Asked why he came to protest, Abu Mushtaq al-Awadi said: "We have rights, and we are demanding our rights.