Tens of thousands of people attended the two-hour rally, according to a police officer.
A group of families of soldiers killed in Iraq stood holding pictures of their loved ones, including one photo of a soldier in full dress uniform lying in a coffin.
More than 3,000 US troops and tens of thousands of Iraqis have been killed since the 2003 invasion of Iraq.
The protest was one of several expected around the country on Saturday, including a large march scheduled in Los Angeles.
Protesters planned co-ordinated efforts during the week to lobby congressmen to take action against the war.
An end to war
Bush's approval ratings stand at one the lowest points of his presidency and polls show a majority of Americans disapprove Bush's plan to send an additional 12,500 troops to Iraq.
Asked about the protests, Gordon Johndroe, a White House national security adviser, said: "Bush understands that Americans want to see a conclusion to the war in Iraq and the new strategy is designed to do just that."
Protesters said they hoped to send Bush and congress a message that Americans did not support the war.
"I'm so sad we have to do this - that we did not learn from the lessons of the Vietnam war"
Jane Fonda, former actress
"I'm convinced this is Bush's war. He has his own agenda there," said Anne Chay, holding a sign with a picture of her 19-year-old son, John, who is serving in Iraq. "We're serving no purpose there."
Chay said her son, who has been in Baghdad since last July, said he was proud of her for traveling from Andover, Massachusetts, to take part in the anti-war rally.
Jane Fonda, a former actress, who was criticised for her opposition to the Vietnam war, drew huge cheers when she addressed the crowd. She noted that she had not spoken at an anti-war rally in 34 years.
"Silence is no longer an option," she said. "I'm so sad we have to do this - that we did not learn from the lessons of the Vietnam war."
John Conyers, a Michigan Democrat and chair of the House Judiciary Committee, said the November 7 election - which gave Democrats control of both houses of Congress - showed Americans want change.
"It takes the ... outrage of the American people to force Washington to do the right thing," he said.
"We've got to hold more of these ... until our government gets the message - Out if Iraq immediately. This year. We've got to go."