Police found the injured 18-year-old after they were called to Hertford Road, Enfield, on Saturday at 22:30 BST over reports of a fight.
He was taken to hospital but was pronounced dead an hour later. Two others also suffered stab wounds.
In a separate incident, a man was shot and stabbed to death in broad daylight near Bow Road Tube station.
The victim, 41, was killed in Eagling Close on Saturday afternoon in what police described as a "violent murder".
Two men have been arrested and are in custody at east London police stations.
The two teenagers who were stabbed in Enfield were found in Palmers Lane.
The 17 and 19-year-olds were taken to hospital but their injuries are not being treated as life-threatening.
Scotland Yard said no arrests have been made and have appealed for witnesses.
In another incident earlier, a man was taken to hospital in a life-threatening condition after being stabbed in the head and neck in Enfield.
Police said they believe the victim, who is thought to be aged in his 30s, was attacked following an "altercation" with a group of men in Exeter Road.
No arrests have been made.

The image of Saffiyah Khan has been shared thousands of times since it was taken at Saturday's demonstration.
Ms Khan, from Birmingham, said she felt moved to intervene when she saw another woman surrounded by about 25 men.
"I don't like seeing people getting ganged up on in my town," she said.
Ms Khan, who said she was not part of an organised counter-protest, told the BBC she had been "quite surprised" when the photo was retweeted around the world.
She said she had initially been happy "to stay out of the way", but "stepped forward" when another woman shouted "Islamophobe" at members of the EDL who had gathered in Centenary Square.
"A group of 25 quite big-looking EDL lads, they surrounded her," she said.
"She was 360 surrounded... I stepped forward and identified myself as someone who supported her and contradicted them."
After that, Ms Khan said, protestors gathered around her instead, which led to the scene captured by a Press Association photographer.
Ms Khan, who was born in the UK and is half-Pakistani, half-Bosnian, said she "wasn't intimidated in the slightest".
She added: "He put his finger in my face. It was very aggressive. A police officer was there and the man took his finger out of my face. I wouldn't have responded violently."
The picture was shared by, among others, Piers Morgan, who called it "photo of the week", and Birmingham Labour MP Jess Phillips.
The BBC has been unable to reach the EDL for comment.
A man has been stabbed to death and two others injured during a large brawl in north London.
[NEXT_CONCEPT]
A viral photo of a woman smiling at an English Defence League (EDL) protester in Birmingham was snapped after she stepped in to defend a "fellow Brummie", she has told the BBC.