The trial opened on 25 January before the court of justice in the southern Paris suburb of Evry.
After more than three months of deliberation, the court reportedly ruled on that it did not have the jurisdiction to judge a case involving the wartime actions of the US government.
Tran To Nga, a former journalist born in 1942 in what was then French Indochina, accused the chemical firms - including Monsanto and Dow Chemical - of causing grievous harm to her and others by selling Agent Orange defoliant to the US government, which used it to devastating effect during the war.
She also accused them of causing damage to the environment.
French court dismisses landmark case against the U.S. makers of Agent Orange https://t.co/hYEEifnJXL
— The Washington Post (@washingtonpost) May 10, 2021
Acting on orders
Dismissing the case, the court said that the companies were acting "on the orders" of the US government which was engaged in a "sovereign act".
NGOs estimate that four million people in Vietnam, Laos and Cambodia were exposed to the 76 million litres of Agent Orange sprayed by US forces to destroy ground cover and food sources in its battle with Communist North Vietnamese troops between 1962 and 1971.
Vietnam 'Agent Orange' trial against chemical companies opens in France
Tran To Nga suffers from typical Agent Orange effects, including type 2 diabetes and an extremely rare insulin allergy.
One of her daughters died of a malformation of the heart.
The multinationals have long argued that they could not be held responsible for the use the American military made of their product.
