The Organisation for the Prohibition of Chemical Weapons did not name the nerve agent as Novichok, but said it agreed with the UK's findings on its identity.
Russia has denied it was behind the attack on Sergei and Yulia Skripal in Salisbury, as Theresa May has claimed.
Foreign Secretary Boris Johnson said: "There can be no doubt what was used."
He added: "There remains no alternative explanation about who was responsible - only Russia has the means, motive and record."
A team from the OPCW visited the UK on 19 March, 15 days after the Skripals were found slumped on a park bench in Salisbury and taken to hospital, along with a police officer who was among the first on the scene.
Ms Skripal was discharged from hospital on Monday but the 33-year-old has said her father is "still seriously ill".
The OPCW said it received information about the medical conditions of the Skripals and Det Sgt Nick Bailey, it collected their blood samples, and it gathered samples from the site in Salisbury.
Mr Johnson said the UK had invited the OPCW to test the samples "to ensure strict adherence to international chemical weapons protocols".
What are Novichok agents?
The name Novichok means "newcomer" in Russian, and applies to a group of nerve agents developed by the Soviet Union in the 1970s and 1980s.
Novichok's existence was revealed by chemist Dr Vil Mirzayanov in the 1990s, via Russian media. He says the nerve agents were designed to escape detection by international inspectors.
Novichok agents are liquids, although others are thought to exist in solid form and could be dispersed as an ultra-fine powder.
Some of the agents are also said to be "binary weapons", meaning the nerve agent is typically stored as two less toxic chemical ingredients that are easier to handle.
When these are mixed, they react to produce the active toxic agent which can cause convulsions, shortness of breath, profuse sweating and nausea.
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