The body of PC Keith Palmer, killed in the Westminster attack, is lying in rest at the Palace of Westminster ahead of his funeral on Monday.
The Queen has consented to the rare honour for the officer.
PC Palmer, 48, was guarding the Houses of Parliament when he was stabbed by Khalid Masood, who had driven into crowds on nearby Westminster Bridge.
Five victims died in the attack on 22 March, during which Masood was shot dead by police.
PC Palmer, who was married with a five-year-old daughter, had served in the Metropolitan Police for 15 years.
Crowds gathered outside the Palace of Westminster to pay their respects as a group of officers wearing white gloves met the hearse.
The guard of honour was formed by officers on PC Palmer’s team at the Parliamentary and Diplomatic Protection Command.
Draped in a police flag, his coffin was taken to the Chapel of St Mary Undercroft, where it will lie in rest for 24 hours.
Inside, a short private service to receive the body into the chapel was led by the Rev Prebendary Rose Hudson-Wilkin and attended by members of the Palmer family.
The command officers will watch over his coffin throughout the night.
The honour of lying in rest in Parliament has in the past been reserved for senior politicians – most recently Baroness Thatcher and Tony Benn.
On Monday, shortly before 13:30 BST, PC Palmer’s body will be accompanied by a special escort to Southwark Cathedral for a full police funeral.
The fifth victim of the attack, Romanian Andreea Cristea, 31, who fell into the River Thames, died in hospital on Thursday.
The other victims were Aysha Frade, 44, who worked at a London sixth-form college, US tourist Kurt Cochran, 54, from Utah, and retired window cleaner Leslie Rhodes, 75, from south London.
Romanian ambassador to the UK, Dan Mihalache, said it was thought Masood’s car had mounted the pavement and hit Ms Cristea’s boyfriend Andrei Burnaz before pushing her into the river.
Relatives of those killed joined members of the Royal Family at a “service of hope” at Westminster Abbey on Wednesday.