Dawn Sturgess, 44, died in hospital Sunday evening, the Metropolitan Police said in a statement.
Sturgess and a 45-year-old man both took ill at a residential address in Amesbury on June 30. The man remains in critical condition in hospital.
Laboratory tests previously confirmed that Sturgess and the man were exposed to the nerve agent after touching a contaminated item with their hands.
Police say they continue to investigate how the pair came to be exposed to the Novichok, the same kind of toxin used in the attack on former Russian spy Sergei Skripal and his daughter Yulia back in February.
The Skripal attack took place in the city of Salisbury, just a few kilometres away from the site of the Amesbury poisoning incident.
WATCH: U.K. Defence Secretary says Russia ‘committed an attack’ leading to death of woman from Novichok
“This terrible news has only served to strengthen our resolve to identify and bring to justice the person or persons responsible for what I can only describe as an outrageous, reckless and barbaric act,” said Neil Basu, chief of the Metropolitan Police’s counter-terrorism division.
“Detectives will continue with their painstaking and meticulous work to gather all the available evidence so that we can understand how two citizens came to be exposed with such a deadly substance that tragically cost Dawn her life.”
WATCH: British police say couple “handled contaminated item”
Police continue to investigate whether the attempted murders of the Skripals are linked to the poisoning of Sturgess and the man.
Britain has openly accused Russia of being responsible for poisoning the Skripals with Novichok, a family of advanced nerve agents developed by the Soviet Union in the 1970 and 1980s.
WATCH: Theresa May offers condolences to Novichok victim, says murder investigation ongoing
Russia denied any involvement in the Skripal incident, and suggested that British police had orchestrated it to stoke anti-Russia sentiments.