Iraqis have been staging weekly protests since July. The movement that stemmed from exasperation over power cuts in the searing summer heat gradually led to broader demands for political reform.
Prime Minister Haider al-Abadi, with backing from the country's most revered Shiite religious cleric, announced a reform package but change has been slow to materialize and the protests have continued, AFP reported.
"Baghdad will no longer be silent," chanted thousands of protesters in the capital's Tahrir (liberation in Arabic) Square.
The demonstration, held under heavy protection from the police and army passed off without incident.
Several smaller protests were also held in other cities, including the main southern hub of Basra, the Shiite shrine city of Karbala and Nasiriyah.