The 49-year-old, who has been named locally as Wayne Broadhurst, was treated by paramedics but died at the scene. A second man, 45, was hospitalised with life-changing injuries and a boy, 14, sustained non life-threatening or changing stab wounds, police said.
An Afghan national, 22, was Tasered and arrested on suspicion of murder and attempted murder at Midhurst Gardens, Uxbridge, at 17:00 GMT on Monday.
The Home Office confirmed the arrested man entered the UK in a lorry in November 2020, was granted asylum and leave to remain in 2022, and does not live in Home Office accommodation.
He was taken to hospital as a precaution but has since been taken into police custody, the Met said.
The attack is not being treated as terrorism, and detectives are working to establish any relationship between the suspect and the three victims, the Metropolitan Police said
Footage posted online appeared to show the suspect walking along a residential street, before two police officers sprinted after him, one pointed a Taser and shouted "drop the knife" and "get on the floor".
Several others joined them before the Taser was fired and the man fell to the ground.
Ch Supt Jill Horsfall said: "This was a shocking and senseless act of violence that has left one man dead and two others injured.
"Our thoughts are with the victim's family and friends at this unimaginably difficult time."
