Khalid Masood killed three people and injured scores more after ploughing a car into pedestrians on Westminster Bridge before stabbing Pc Keith Palmer to death.
Here is what we know about the terrorist's victims.
Retired window cleaner Leslie Rhodes was the fourth victim to be named.
The 75-year-old, from Clapham, south London, died at King's College Hospital on Thursday night after life support was withdrawn.
Neighbours described him as a "lovely man" and said the pensioner was a keen music fan.
The innocent casualties include 12 Britons, three French children, two Romanians, four South Koreans, two Greeks, and one each from Germany, Poland, Ireland, China, Italy and the United States.
Kurt Cochran, a US tourist from Utah, was killed on Westminster Bridge after Khalid Masood drove a car into unsuspecting pedestrians.
He and his wife Melissa, on the last day of a trip celebrating their 25th wedding anniversary, were visiting her parents, who are serving as Mormon missionaries in London.
Mrs Cochran was badly injured.
After Mr Cochran's identity was revealed, US President Donald Trump tweeted: "A great American, Kurt Cochran, was killed in the London terror attack. My prayers and condolences are with his family and friends."
Aysha Frade, who worked in administration at independent sixth-form school DLD College London in Westminster, also died on the bridge.
She is understood to have been 43 and married with two daughters.
At least 100 people attended a memorial in Spain to commemorate the British national.
A minute's silence was held in the Galician municipality of Betanzos, where Mrs Frade's family originates and where she spent her summers.
Betanzos councillor Andres Hermida said the community in Spain was in "enormous pain" and shrouded in an "atmosphere of sadness".
He told the Press Association: "We had a minute's silence in the Plaza de la Constitucion outside the local government building and we have declared three days of mourning, which will include flying the flag at half mast until Saturday.
"About 100 people attended despite the rainy weather."
Mrs Frade's family is well known in Betanzos, where her older sisters, Silvia and Michelle, run the Notting Hill English language academy.
Pc Keith Palmer
Pc Keith Palmer, a 48-year-old husband and father and Charlton Athletic season ticket-holder, was stabbed to death in the attack.
He has been praised as a "strong, professional public servant" who served in the military before joining the Metropolitan Police's parliamentary and diplomatic protection command.
Pc Palmer served as a reservist from August 1987 to August 2001, leaving as a bombardier, and had 15 years of service as a police officer.
Charlton Athletic said Pc Palmer was "a true hero who will be greatly missed by all the Charlton family".
Portuguese pedestrian Francisco Lopes, 26, has said he was "scared for my life" after being mowed down on Westminster Bridge, leaving him with leg and hand injuries.
He said: "He started to move towards the pedestrian pavement and started to just take out the people that were in front of the car, so, literally when I realised this, the car was literally just about one metre away, so I had no, literally, no time to get out of the way."
Travis Frain, 19, was walking across Westminster Bridge with other youngsters when he was mowed down by the terrorist's 4x4.
Angela Frain, from Darwen, Lancashire, said her son escaped with his life after going over the bonnet of the killer's car as the carnage began.
Seconds later, the politics student, who wants to become an MP, called his mother to say: "Mum I'm safe ... I know you will be worrying."
He suffered a fractured leg, fractured left arm, cuts to his thigh and two broken fingers and will be operated on in hospital.
The mother of one of the French students caught up in the attack thought he was dead for an hour before being told he was injured.
The teenager, named only as Thomas, was one of three pupils hurt as they walked along the bridge during a school trip to London.
He suffered a head injury and fractures to his legs, his mother told French media.
The students, aged between 15 and 16, were pupils from Lycee Saint-Joseph de Concarneau, Brittany.
His mother told Brittany website Le Telegramme: "It was the school who told us Wednesday afternoon that the attack had taken place and our son was one of the victims."
Andreea Cristea and Andrei Burnaz
Andrei Burnaz and Andreea Cristea, 29, were on the bridge when the car ploughed into them
Miss Cristea was thrown into the River Thames, and subsequently suffered a blood clot on the brain for which she was operated on.
According to reports the couple were in London celebrating Mr Burnaz's birthday, and he was due to propose to Ms Cristea later that day.
Mr Burnaz suffered a broken foot, and Ms Cristea was in a stable condition after surgery.
An Italian woman who was on holiday in the capital was hit by the terrorist's car, the country's embassy in London said.
The woman, who suffered fractures, was in a stable condition the day after the attack, the embassy added.
A Chinese tourist sustained minor injuries in the attack, a spokesman for the Chinese foreign ministry said.
A Polish man suffered minor injuries and was released from hospital on Thursday, the country's embassy said.