The 27-year-old man was arrested after being spotted by a member of the public.
Detective Inspector Ian Lott from the Homicide and Major Crime Command called the murder “a devastating attack on two women in their homes”.
“Following a recent media appeal a discerning member of the public alerted police to a real time sighting and officers moved quickly to detain and arrest the man wanted for questioning,” he said.
Police said the investigation into the circumstances around the murders is ongoing.
Officers were called to an address in northwest London just before 9pm on Friday following reports two women had been seriously injured.
The victims, aged 33 and 66, were pronounced dead at the scene in Golders Green Crescent.
Formal identification has yet to take place, but police say they are confident they know their identities and their next-of-kin have been informed.
Police have urged anybody who saw anything in the area on Friday night to get in touch with investigators immediately.
Anyone with information is asked to call the incident room on 0208 358 0200 or anonymously call Crimestoppers on 0800 555 111.