Lennon had a profound influence on rock and roll and in expanding the genre's boundaries during the 1960s. He is widely considered, along with songwriting partner Paul McCartney, as one of the most influential singer-songwriter-musicians of the 20th century. Many of the songs written by Lennon, however, are more introspective — often in the first person — and more personal than McCartney's. His most surreal pieces of songwriting, "Strawberry Fields Forever" and "I Am the Walrus", are fine examples of his unique style. Lennon's partnership in songwriting with McCartney many times involved him in complementing and counterbalancing McCartney's upbeat positive outlook with the other side of the coin, as one of their songs, "Getting Better" demonstrates.

Lennon often spoke his mind freely and the press was used to querying him on a wide range of subjects. On March 4, 1966 in an interview for the London Evening Standard with Maureen Cleave, who was a friend of his, Lennon made an off the cuff remark regarding religion. The article was printed and nothing came of it, until five months later when a teen magazine called Datebook reprinted the words "I don't know what will go first—Rock and Roll or Christianity. We're more popular than Jesus now," on the front cover.

A firestorm of protest swelled from the southern U.S. Bible Belt area, as conservative groups publicly burned Beatles records and memorabilia. Radio stations banned Beatles music and concert venues cancelled performances. Even The Vatican got involved with a public denouncement of Lennon's comments. On August 11, 1966, the Beatles held a press conference in Chicago, Illinois, in order to address the growing furor.

The governing members of the Vatican accepted his apology and the furor eventually died down, but constant Beatlemania, mobs, crazed teenagers, and now a press ready to tear them to pieces over any quote was too much to handle. The Beatles soon decided to stop touring, and indeed, never performed a scheduled concert again. From this point onward the Beatles were a studio band (perhaps the first ever). Freed from the problem of having to compose music they could recreate live on stage, they could explore the technological limits of music and create unique and original sounds.

On November 9, 1966, after their final tour ended and right after he had wrapped up filming a minor role in the film How I Won the War, Lennon visited an art exhibit of Yoko Ono's at the Indica art gallery in London. Lennon began his love affair with Ono in 1968 after returning from India and leaving his estranged wife Cynthia, who filed for divorce later that year. Lennon and Ono were from then on inseparable in public and private, as well as during Beatles recording sessions. The press was extremely unkind to Ono, posting a series of unflattering articles about her, one even going so far as to call her "ugly." This infuriated Lennon, who rallied around his new partner and said publicly that there was no John and Yoko, but that they were one person, JohnAndYoko. These developments led to friction with the other members of the group, and heightened the tension during the 1968 White Album sessions.

Some Beatles fans blame Ono for the Beatles' breakup, but the band had been growing apart almost immediately after the death of their manager Brian Epstein in 1967. Lennon in particular cited Epstein as the glue which had held them all together.