Some advocates within the peace movement advocated a unilateral withdrawal of U.S. forces from Vietnam. One reason given for the withdrawal is that it would contribute to a lessening of tensions in the region and thus less human bloodshed. Early opposition to U.S. involvement in Vietnam was centered around the Geneva conference of 1954. American support of Diem in refusing elections was thought to be thwarting the very democracy that America claimed to be supporting. John Kennedy, while Senator, opposed involvement in Vietnam.

Opposition to the Vietnam War tended to unite groups opposed to U.S. anti-communism, imperialism and colonialism and, for those involved with the New Left such as the Catholic Worker Movement, capitalism itself. Others, such as Stephen Spiro opposed the war based on the theory of Just War. Some wanted to show solidarity with the people of Vietnam, such as Norman Morrison emulating the actions of Thích Quảng Đức. Some critics of U.S. withdrawal predicted that it would not contribute to peace but rather vastly increase bloodshed. These critics advocated U.S. forces remain until all threats from the Viet Cong and North Vietnamese Army had been eliminated. Advocates of U.S. withdrawal were generally known as "doves", and they called their opponents "hawks", following nomenclature dating back to the War of 1812.

High-profile opposition to the Vietnam War turned to street protests in an effort to turn U.S. political opinion. On October 15, 1969, the Vietnam Moratorium attracted millions of Americans.

The fatal shooting of four anti-war protesters at Kent State University led to nation-wide university protests. Riots broke out at the 1968 Democratic National Convention.

After explosive news reports of American military abuses, such as the 1968 My Lai Massacre, brought new attention and support to the anti-war movement, some veterans joined Vietnam Veterans Against the War.

Anti-war protests ended with the final withdrawal of troops after the Paris Peace Accords were signed in 1973. South Vietnam was left to defend itself alone when the fighting resumed. Many South Vietnamese fled to the United States in one of the largest war refugee migrations in history.