Police were called to Essex Road at 5.30pm on Saturday where they found the man, aged in his 50s, with stab wounds.
The victim was treated by paramedics but he was pronounced dead at 17:58pm.
Residents said the man was a local flower seller who was trying to stop a mugging when he was stabbed.
Police said his family has been informed.
An air ambulance was pictured landing near the scene before the man was pronounced dead.
In a statement, the Metropolitan Police said: "Police were called at 17:27hrs on Saturday, 29 May to reports of an injured man on Essex Road, N1.
"Officers attended and found a man suffering from a stab wound and immediately provided first aid.
"Despite their efforts, and that of the London Ambulance Service, the man, believed to be aged in his 50s, was pronounced dead at the scene at 17:58hrs."
No arrests have been made and a crime scene remains in place, authorities said.
It comes following a number of stabbings across the capital in recent weeks.
On Saturday a 21-year-old man was left with potentially life-changing injuries after he was stabbed in Plumstead in the early hours of the morning.
Police were called at around 1.30am to reports that two men had been stabbed in Plumstead High Street. Officers attended the scene and located two men, aged 21 and 23 years, who were suffering from stab injuries.
Detectives want to speak to two men after a 19-year-old was knifed near Sadiq Khan’s office in Southwark, south London.