“This morning a 51-year-old German woman died after being treated in a critical condition in hospital,” a Spanish civil defence agency stated.
It is not yet clear which of the twin terrorist attacks she was injured in.
Many people were injured in the first attack on 17 August, when a van drove into crowds of people on the famous tourist boulevard of Las Ramblas.
Just hours later there was a similar attack in the seaside resort of Cambrils, about 70 miles southwest of Barcelona.
Spanish authorities are continuing to investigate the attacks, which injured 120 people. Six remain in a critical condition and five others have serious injuries.
On Saturday, hundreds of thousands of people marched in Barcelona in an act of solidarity following last week’s attacks.
In an unprecedented move, King Felipe VI also took part, along with the Spanish Prime Minister and the local mayor.
Those who helped the victims, including the emergency services, taxi drivers and shopkeepers, were at the head of the march, as the crowds stretched back a mile.
Red, yellow and white roses were handed out – the colours associated with the Spanish city – and a sea of Catalan flags could be seen far into the distance.
People of all ages and ethnicities waved banners which read “we are not afraid” and “the best response is peace”.