Police arrested a 45-year-old man on suspicion of attempted murder in the attack.
The Metropolitan Police said the attack in the Golders Green area left two men, aged 34 and 76, hospitalised with knife wounds.
Counter-terror police are investigating whether the stabbings are linked to recent arson attacks on synagogues and other Jewish sites in the United Kingdom capital.
Politicians condemned the attack.
"Attacks on our Jewish community are attacks on Britain," Prime Minister Keir Starmer said.
The security organisation Shomrim said a suspect "was seen running along Golders Green Road armed with a knife and attempting to stab Jewish members of the public".
It said the suspect was detained by Shomrim members and arrested by police, who used a stun gun on him.
Surveillance camera footage showed a man beside a bus stop donning a kippah, or traditional skullcap, before a passerby with a knife lunges at him.
Police said the suspect also tried to stab police officers but none was injured.
They are working to establish the suspect's citizenship and background, and Detective Chief Superintendent Luke Williams said "investigators are considering all possible motives".
Arson attacks in recent weeks targeted Jewish sites in London, including a charity's ambulances in Golders Green and a synagogue a few kilometres away.
"It happens in Israel but happening on our own doorstep, of course it's shocking," said Golders Green resident Moishe Grunfeld.
"I have kids, I have grandchildren."
The UK's Jewish community is long-established but tiny as a percentage of the population, numbering about 300,000.
The northwest London suburb of Golders Green is one of its epicentres - home to kosher restaurants, Jewish schools and several dozen synagogues, as well as large Asian and Middle Eastern communities.
"There must be absolutely no place for anti-Semitism in society," London Mayor Sadiq Khan said.
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