The blue English Heritage plaque adorns a Georgian row house at 34 Montagu Square, where the couple lived in 1968.
The ground floor and basement apartment was home to several rock legends. Beatles drummer Ringo Starr bought the property in 1965, and he sublet it to Paul McCartney and later Jimi Hendrix before Lennon and Ono moved in.
It was the setting for the nude photo of the couple on the cover of their "Two Virgins" album.
Ono said Saturday she was honored by the decision to erect the plaque, one of hundreds across London marking the homes of prominent figures.
Lennon would have turned 70 on Oct. 9. He was shot dead in New York in December 1980.