Islamic State fanatic Ali Harbi Ali, 26, carried out the “cold and calculating” murder at the veteran MP’s constituency surgery in Leigh-on-Sea, Essex, on October 15, 2021.
He told the Old Bailey trial he had no regrets about the murder, defending his actions by saying Sir David deserved to die as a result of voting in Parliament for air strikes on Syria in 2014 and 2015.
A jury deliberated for just 18 minutes to find Ali guilty of murder and preparing for terrorist acts.
Mr Justice Sweeney said Ali, who refused to stand up in the dock on “religious grounds” as he was convicted, would be sentenced on Wednesday (April 13).
Sir David’s family sat in the well of the courtroom as the verdicts were delivered, just metres from Ali in the dock.
Director of Public Prosecutions Max Hill QC said the murder was “the most appalling tragedy”, particularly for the Amess family, and an “attack on democracy”.
He said: “I’m obviously pleased that at the end of what must have been a very difficult trial for Sir David Amess’s family, justice has been served and this individual will now pay the price for his crimes.”
The court heard how London-born Ali had become self-radicalised in 2014, going on to drop out of university, abandoning ambitions for a career in medicine.
The defendant, who came from an influential Somali family and said he had a childhood “full of love and care”, considered travelling to Syria to fight but by 2019 opted for an attack in Britain.
Ali bought a £20 knife from Argos six years ago which he carried in his bag throughout the summer of 2021 as he “scoped out” possible targets, jurors heard.
On the morning of October 15, Ali, from Kentish Town, north London, was caught on CCTV as he made his way by foot and train to Essex.
Within minutes of meeting Sir David, Ali pulled out a 12in carving knife and stabbed him more than 20 times.
He waved the bloody knife and threatened to kill the MP’s two female aides and a couple who had arrived for their appointment.
Sir David’s assistant Julie Cushion told jurors he appeared “self-satisfied” in the wake of the brutal killing.
In police interview, he spoke calmly about his terror plot and admitted allegiance to so-called Islamic State.
He told officers Sir David immediately suspected a “sting”, having been duped into talking about a fake drug “cake” in the television series Brass Eye.
He went on: “I felt like one minute I was sat down at the table talking to him and the next he was, sort of, dead.
“But, yeah, it’s probably one of the strangest days… of my life now, y’know?”
Jurors were told Ali had no mental health issues and he accepted much of the evidence against him.
Sir David was killed five years after Batley and Spen MP Jo Cox was murdered in her constituency.
His death led to renewed concern around the safety of MPs.