Dawn Sturgess, aged 44, died in hospital last night, while her partner Charlie Rowley, 45, who was also exposed to the deadly chemical, remains in hospital in a critical condition.
Metropolitan Police Assistant Commissioner Neil Basu, the UK's most senior counter-terrorism office, said Ms Sturgess and Mr Rowley were the only people to have presented with confirmed symptoms of Novichok exposure since the attack on the Skripals and the subsequent illness of police officer Nick Bailey are he too came into contact with the substance.
The police are working to ensure that her family have all the necessary support that they need at this extremely hard time. That afternoon, Rowley fell ill at the same address in Amesbury and was also hospitalised. Russian Federation has repeatedly urged London to conduct a proper and transparent investigation and dismissed baseless allegations of its involvement.
Home Secretary Sajid Javid visited Salisbury today where he said he is "confident police and counter-terrorism forces will 'eventually get to the bottom" of what happened.
He said no one else in the area has shown any sign of Novichok poisoning.
Assistant Commissioner Neil Basu, head of United Kingdom counter-terrorism policing, which is leading the investigation, said he was "unable to say" if the incident in Amesbury is linked to the poisoning of the Skripals on March 3 - but it is their "main line of inquiry".
"Detectives are working as quickly and as diligently as possible to identify the source of the contamination, but this has not been established at this time", police said on Sunday. She said: "The staff here at Salisbury District Hospital worked tirelessly to save Dawn".More news: Trump names Supreme Court nominee
Shortly after the news of Sturgess' passing broke, British Prime Minister Theresa May issued a statement saying that she is "appalled and shocked" by the development, while extending her condolences to the woman's family.
The couple, who were heavy drinkers and drug takers, are believed to have picked up a syringe or vial of the nerve agent dumped by the assassins sent to kill Sergei Skripal and his daughter Yulia.
The BBC has reported that the risk of Novichok contact to the general public remains low.
Per CNN, authorities now believe that Sturgess and Rowley came into contact with a contaminated item via their hands, but now lack the ability to determine whether the poison is from the same batch that the Skripals ingested.
Sergei and Yulia Skripal were both discharged from hospital in May and have been offered permanent close protection - as well as a possible settlement in the USA or Australia. Police are investigating the death of Sturgess, a mother of three children, as a homicide.
Police said they could not yet say whether the nerve agent in the Amesbury case was linked to the Salisbury attack - but it was their main line of inquiry. "We consider that it is a danger not only for the British, but for other Europeans", Kremlin spokesman Dmitry Peskov told reporters Monday.
On Monday, Britain's counterterrorism chief announced that investigators had determined that it was "highly likely" that this Novichok was indeed from the same batch.