The 21-year-old victim died at Brent Cross Shopping Center on Tuesday evening, despite the efforts of police, paramedics and members of the public.
Police were called to the North West London Shopping Center at 6:45 p.m. after men clashed.
An 18-year-old man was arrested nearby on suspicion of murder, while a second man – also suspected of being 18 – was arrested on suspicion of a clash.
Chief Superintendent Sara Leach of the Metropolitan Police said: “My thoughts are with the loved ones of the young man who was killed in this incident.
“I want to thank the members of the public who came to his aid. They have shown considerable courage.
“Two people have been arrested and an investigation is already underway. We will do our utmost to identify and bring to justice those responsible.
“The public can expect to see an increased police presence in the region for the remainder of this evening and in the days to come. “
A number of people likely witnessed the stabbing, police said, adding that anyone with information should call 101, providing reference CAD6136 / 04MAY.