Four people, including the police officer and the attacker, died. At least 40 people were injured, including three other officers. Paramedics fought to save his life, and that of his victim, on the floor of the cobbled courtyard in front of Parliament. Mr Ellwood - whose brother died in the Bali terrorist bombing in 2002 - was among those who rushed to help and attempted mouth-to-mouth resuscitation of injured PC Palmer. His friend of 20 years, Conservative MP Adam Afriyie, told the BBC he saw him heading towards the scene despite police instructions to rush to safety.
In pictures: 'Terrorist incident' at Westminster Eyewitnesses described scenes of panic as the attacker was shot several times as he approached a second police officer close to the Houses of Parliament.
Latest updates: Westminster attack
Four dead in Westminster attack
Photographs showed the MP's bloodied hands and face as he applied pressure to the officer's wounds.
His actions attracted admiration from his Westminster colleagues. Conservative MP Ben Howlett tweeted: "Tobias Ellwood is an absolute hero for what he did to help the policeman this afternoon!" Meanwhile, Liberal Democrat leader Tim Farron said: "Today, Tobias gave MPs a good name.
"He was utterly heroic, pure and simple. He went above and beyond and did all he could to save a police officer." The Bournemouth East MP is a Foreign Office minister, with the Middle East, Africa and counter terrorism listed among the areas within his brief.