Demonstrators had gathered outside the White House before heading toward the US Capitol building.
The demonstrations come days after General David Petraeus, the senior US commander in Iraq, testified to the US congress on conditions in Iraq.
Viviana Hurtado, Al Jazeera's correspondent in Washington DC, said the anti-war demonstration was attended by people from a wide variety of backgrounds.
"One of the differences with this demonstration is that it is being led by Iraqi war veterans," she said.
Phil Aliff, 21, marched as a member of Iraq Veterans Against the War.
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"I stayed [in Iraq] for a year, in Abu Ghraib and outside Fallujah," he said.
"When we arrived, we were told we were here to bring stabilisation to the country.
"But we were not rebuilding anything. The Iraqis had only two hours of electricity. And I saw the atrocities committed by the Americans there."
The arrests came after several dozen protesters carried out a "die-in", lying on their backs in front of congress in an attempt to draw attention to the rising death toll in Iraq.
Many were arrested without a struggle after they jumped over a waist-high barrier.
But some grew angry as police with shields and riot gear attempted to push them back and police used chemical spray on at least two people.
Relatives of soldiers who are serving or had served in Iraq were a key group within the public demonstration.
Diane Santoriello held a photograph of her son Neil, who was killed in Iraq in August 2004.
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time low [Reuters]
"I am here to get congress to de-fund the war," she said.
Brian Becker from the Answer (Act Now to Stop War and End Racism) coalition, the group organising the anti-war march, said Iraqi civilians wanted US forces out of their country.
"The vast majority of the people in the US want the war ended and the troops brought home now," he said.
Speakers at the anti-war demonstration included Cindy Sheehan, an activist whose son was killed while serving in Iraq.
US public support for the war is at an all-time low, with 62 per cent of Americans believing that invading Iraq was a mistake, according to a New York Times/CBS poll published last week.
Counter-protesters gathered near the anti-war march, frequently chanting "U-S-A" and waving US flags.
Retired Air Force Lt. Col. Robert 'Buzz' Patterson, speaking from a stage to crowds of people clad in camouflage, American flag bandanas and Harley Davidson jackets, said he wanted to send three messages.
"Congress, quit playing games with our troops. Terrorists, we will find you and kill you," he said.
"And to our troops, we're here for you, and we support you."