Roger Buckingham, 31, was given an automatic sentence of life in prison for the murder of Piotr Mikiewicz, the Evening Standard reported. London Recorder Brian Barker imposed a minimum of 27 years to be served before parole.
Barker called the crime "a shocking waste of life."
"Mr. Mikiewicz was a brave man who acted beyond the call of duty," Barker said.
"He ignored his own safety and he paid for his actions with his life. He was truly an exceptional man."
Mikiewicz, 40, a Polish immigrant who had recently married, was working in the quiet suburban neighborhood of Shepherd's Bush when he heard an alarm go off. He spotted Buckingham running down the driveway and tried to block him, hitting him several times with a broom.
Investigators said Buckingham, who was addicted to crack cocaine, stabbed Mikiewicz several times with a kitchen knife and then, when his getaway car failed to start, finished the job by plunging the knife in deep. Buckingham fled the scene, throwing the knife into the river, but was arrested 24 hours later.
During the trial, Buckingham's lawyer argued the killing was not intentional.
"He had a laudable sense of civic duty and of right and wrong and it was to cost him his life," the prosecuting lawyer, Aftab Jafferjee, said of Mikiewicz.