The violence, which mostly struck during morning rush hour amid tightened security ahead of the polls, also wounded more than 270 people.
Officials said bombings hit 12 different areas of Iraq, leaving 37 dead and making Monday the country's deadliest day since March 19.
No group immediately claimed responsibility for the attacks, but militants linked to Al-Qaeda frequently attack both government targets and civilians in a bid to destabilize the country, and have reportedly sought to intimidate candidates and election officials ahead of polling.
The deadliest attacks were in Baghdad, where eight bombings struck in seven neighborhoods across the capital despite tougher checkpoint searches and heightened security.
Among them was a car bomb in a parking area used by vehicles making their way to Baghdad's heavily-guarded airport, a rare bombing on the road famously known as "Route Irish".
In all, 21 people were killed and 73 wounded in the capital, officials said.
In Tuz Khurmatu, 175 kilometres (110 miles) north of Baghdad, six people were killed and 67 wounded by three near-simultaneous car bombs, and in Kirkuk, five people were killed and 44 wounded by six more car bombs.
Attacks elsewhere in Iraq killed five people and wounded 89 others.