Fans view George Harrison’s lead guitar as a key element in the Fab Four’s success, but according to a new book, Harrison took a backseat on many of the band’s greatest guitar songs — from “Day Tripper” to “Birthday.”

He didn’t play even a lick on large swaths of the groundbreaking album “Sgt. Pepper’s Lonely Hearts Club Band,” opting for harmonica, congas, comb-and-paper in studio sessions while dutifully practicing the sitar at home three times daily.

In “George Harrison: Behind the Locked Door,” author Graeme Thomson quotes singer Peter Frampton in 1971: “I said, ‘Can I put on some Beatles tracks and ask you about them?’ And [Harrison] said, ‘Sure.’ I’d put on ‘Paperback Writer’ and say, ‘I love the guitar part on that,’ and he’d say, ‘Oh, that’s Paul.’ I was embarrassed. I said, ‘I’m sorry,’ and he said, ‘It’s OK, it’s OK.’ He was very sweet about it, but it wasn’t until that particular moment that I realized he was stifled.”

In re-examining the Quiet One’s remarkable life, Thomson argues that George Harrison’s flashes of supreme musicianship were uneven and in line with his “comically contradictory” ways, such as the time he visited producer George Martin on his sickbed and presented him with a statuette of Ganesh to signify pleasure in the smallest of things — before roaring off in a McLaren F1 sports car capable of 230 mph.

“The routine paradoxes evident in most humans seemed in Harrison to be amplified,” Thomson writes. “Just as the success of the Beatles was itself riven by extremes.”

Though Harrison’s “sassy sixth” note on “She Loves You” in the summer of 1963 did as much to spur on Beatlemania as the “yeah, yeah, yeah” of its chorus, the pecking order was clear from the start. Illustrative of this dynamic is a clip featured in the book from British rock newspaper Melody Maker in 1965:

When George asked John Lennon an innocuous question, Lennon responds with: “What do you want?” And after asking him to repeat the question, replied, “Mind your own bloody business. Got a ciggy?” John then helped himself to a cigarette from George’s top pocket before George could reply.

“Lennon and McCartney’s indifference was, in many ways, the making of [Harrison]. It forced him to up his game or else retreat. The irony is Harrison’s refusal to play second fiddle did as much as anything else to hasten the demise of the band,” Thomson writes.

The decade he spent with the Beatles was meteoric. But the full span of George Harrison’s following solo career, his devotion to Hare Krishna, Indian music and fast cars follow another kind of arc.

Thomson begins the 406-page biography under the spotlights of Madison Square Garden, where Harrison coaxed Bob Dylan onstage and led the Concert for Bangladesh on Aug. 1, 1971, considered the first musician-led humanitarian effort.

At the time, Harrison’s “My Sweet Lord” was a No. 1 hit on both sides of the Atlantic, but still he was reticent.

“George playing at [the Concert for] Bangladesh was a very courageous move,” second wife Olivia Harrison told the author. “That really was his contribution, overcoming his self-consciousness to do that.”

Never one to enjoy touring, Harrison disdained fans who would expect him to play “Something” and “Here Comes the Sun,” pushing the issue by staging long instrumentals of Indian music. His first solo release, “All Things Must Pass,” was a commercial success. But Harrison could never replicate it. His 1974 tour was pilloried by critics and poorly attended, and a concert film shot then was scrapped.

While foundering on stage, he hit it big on the screen. He raised millions of pounds to form a production company that rescued the Monty Python movie “Life of Brian,” released in 1979. Harrison, meanwhile, would not hit the road on tour until Eric Clapton offered to lend Harrison his own band in 1991.

By then, Harrison’s isolation from ordinary life was evident. He didn’t even know how to operate a pay phone, the book says.

Bass player Nathan East recalled going to the gym with Beatle George, only to discover “he didn’t know how it worked down there with the lockers. He was not used to public facilities. I had to explain, ‘Here’s the key, put your clothes in there . . .’ ”

Joining forces with Jeff Lynne of Electric Light Orchestra revived Harrison in the early 1990s with hits like “When We Was Fab” and “Got My Mind Set on You,” followed by the formation of super group the Traveling Wilburys with Lynne, Bob Dylan, Roy Orbison and Tom Petty.

His comeback only deepened his relationship with Eastern spirituality, though he never gave up his love for Grand Prix races. He lived in his Henley-on-Thames estate, a 120-room mansion, even after he suffered a serious knife attack by a crazed fan in 2000.

The stress from that attack set in motion, a friend told the author, a string of cancers that would claim his life in 2001.

Through it all, he kept his famous zen, as Eric Idle noted in a speech after his death. “I was on an island somewhere when a man came up to him and said, ‘George Harrison! Oh my God, what are you doing here?’ And he said, ‘Well, everyone’s got to be somewhere.’ ”