Lennon and McCartney started composing "She Loves You" on 26 June 1963 after a concert at the Majestic Ballroom in Newcastle upon Tyne during their tour with Roy Orbison and Gerry and the Pacemakers. They began writing the song on the tour bus, and continued later that night at their hotel in Newcastle[nb 1] eventually completing it the following day at McCartney's family home in Forthlin Road, Liverpool.
In 2000, McCartney said the initial idea for the song began with Bobby Rydell's hit "Forget Him" with its call and response pattern, and that "as often happens, you think of one song when you write another ... I'd planned an 'answering song' where a couple of us would sing 'she loves you' and the other ones would answer 'yeah yeah'. We decided that was a crummy idea but at least we then had the idea of a song called 'She Loves You'. So we sat in the hotel bedroom for a few hours and wrote it – John and I, sitting on twin beds with guitars."
Like many early Beatles songs, the title of "She Loves You" was framed around the use of personal pronouns. But unusually for a love song, the lyrics are not about the narrator's love for someone else; instead the narrator functions as a helpful go-between for estranged lovers:
You think you lost your love,
Well, I saw her yesterday.
It's you she's thinking of –
And she told me what to say.
She says she loves you ...
This idea was attributed by Lennon to McCartney in 1980: "It was Paul's idea: instead of singing 'I love you' again, we'd have a third party. That kind of little detail is still in his work. He will write a story about someone. I'm more inclined to write about myself."
Lennon, being mindful of Elvis Presley's "All Shook Up", wanted something equally stirring: "I don't know where the 'yeah yeah yeah' came from [but] I remember when Elvis did 'All Shook Up' it was the first time in my life that I had heard 'uh huh', 'oh yeah', and 'yeah yeah' all sung in the same song". The song also included a number of falsetto "wooooo"s, which Lennon acknowledged as being inspired by the Isley Brothers' recording of "Twist and Shout", which the Beatles had earlier recorded, and which had also been inserted into the group's previous single, "From Me to You". As Lennon later said: "We stuck it in everything". McCartney recalls them playing the finished song on acoustic guitars to his father Jim at home immediately after the song was completed: "We went into the living room and said 'Dad, listen to this. What do you think? And he said 'That's very nice son, but there's enough of these Americanisms around. Couldn't you sing 'She loves you, yes, yes, yes!' At which point we collapsed in a heap and said 'No, Dad, you don't quite get it!'" EMI recording engineer Norman Smith had a somewhat similar reaction, later recounting, "I was setting up the microphone when I first saw the lyrics on the music stand, 'She loves you, yeah, yeah, yeah, She loves you, yeah, yeah, yeah, She loves you, yeah, yeah, yeah, Yeah!' I thought, Oh my God, what a lyric! This is going to be one that I do not like. But when they started to sing it – bang, wow, terrific, I was up at the mixer jogging around."
The "yeah, yeah, yeah" refrain proved an immediate, infectious musical hook. Unusually, the song starts with the hook right away, instead of introducing it after a verse or two. "She Loves You" does not include a bridge, instead using the refrain to join the various verses. The chords tend to change every two measures, and the harmonic scheme is mostly static.
The arrangement starts with a two-count from Ringo on the drums, and his fills are an important part of the record throughout. The electric instruments are mixed higher than before, especially McCartney's bass, adding to the sense of musical power that the record provides. The lead vocal is sung by Lennon and McCartney, switching between unison and harmony.
George Martin, the Beatles' producer, questioned the validity of the major sixth chord that ends the song, an idea suggested by George Harrison. "They sort of finished on this curious singing chord which was a major sixth, with George [Harrison] doing the sixth and the others doing the third and fifth in the chord. It was just like a Glenn Miller arrangement." The device had also been used by country music-influenced artists in the 1950s. McCartney later reflected: "We took it to George Martin and sang 'She loves you, yeah, yeah, yeah, yeeeeeaah ...' and that tight little sixth cluster we had at the end. George [Martin] said: 'It's very corny, I would never end on a sixth'. But we said 'It's such a great sound, it doesn't matter'." The Beatles: Complete Scores shows only the notes D (the fifth) and E (the sixth) sung for the final chord, while on the recording McCartney sang G (the root) as Harrison sang E and Lennon sang D.