"There is no basis for any of the claims of plaintiffs under the domestic law of any nation or state or under any form of international law," U.S. District Judge Jack B. Weinstein in Brooklyn wrote in a 233-page ruling. "The case is dismissed."
Lawyers who filed the lawsuit on behalf of the Vietnamese citizens argued that Agent Orange, which is laden with the highly toxic chemical dioxin, was a poison barred by international rules of war.
Lawyers for Monsanto, Dow Chemical and more than a dozen other companies said they should not be punished for following what they believed to be the legal orders of the nation's commander-in-chief.
The Department of Justice filed a brief supporting the chemical companies, saying a ruling against the firms had the potential to cripple the president's powers to direct U.S. armed forces in wartime.
"This lawsuit never had a chance," says CBSNews.com Legal Analyst Andrew Cohen. "There just isn't any legal authority to hold these companies responsible for the way their products were used. And an appeal here almost certainly will lose as well."
The civil suit was the first attempt by Vietnamese plaintiffs to seek compensation for the effects of Agent Orange, which has been linked to cancer, diabetes and birth defects among Vietnamese soldiers, civilians and American veterans.
U.S. aircraft sprayed more than 21 million gallons of the chemical between 1962 to 1971 in attempts to destroy crops and remove foliage used as cover by communist forces.
Some 10,000 U.S. war veterans already receive medical disability benefits related to Agent Orange.
The Vietnamese government has said the United States has a moral responsibility for damage to its citizens and environment but has never sought compensation for victims.