Born and raised in Liverpool, Lennon became involved in the skiffle craze as a teenager, his first band, The Quarrymen, evolving into The Beatles in 1960. As the group began to undergo the disintegration that led to their break-up towards the end of that decade, Lennon launched a solo career that would span the next, punctuated by critically acclaimed albums, including John Lennon/Plastic Ono Band and Imagine, and iconic songs such as "Give Peace a Chance" and "Imagine".

Lennon revealed a rebellious nature and acerbic wit in his music, his writing, on film, and in interviews, and became controversial through his work as a peace activist. He moved to New York City in 1971, where his criticism of the Vietnam War resulted in a lengthy attempt by Richard Nixon's administration to deport him, while his songs were adapted as anthems by the anti-war movement. Disengaging himself from the music business in 1975 to devote time to his family, Lennon reemerged in 1980 with a comeback album, Double Fantasy, but was murdered three weeks after its release.

Lennon's solo album sales in the United States alone stand at 14 million units, and as performer, writer, or co-writer he is responsible for 27 number one singles on the US Hot 100 chart.a In 2002, a BBC poll on the 100 Greatest Britons voted him eighth, and in 2008 Rolling Stone ranked him the fifth greatest singer of all time. He was posthumously inducted into the Songwriters Hall of Fame in 1987 and into the Rock and Roll Hall of Fame in 1994.

Lennon was born on 9 October 1940 in Liverpool Maternity Hospital, Oxford Street, Liverpool, to Julia and Alfred Lennon. According to some biographers, a German air raid was taking place, and Julia's sister, Mary "Mimi" Smith, used the light cast by the explosions to see her way as she ran through the blacked-out back roads to reach the hospital. Smith said later, "I knew the moment I saw John in that hospital that I was the one to be his mother, not Julia. Does that sound awful? It isn't, really, because Julia accepted it as something perfectly natural. She used to say, 'You're his real mother. All I did was give birth.'" Lennon was named after his paternal grandfather, John "Jack" Lennon, and Winston Churchill.

Lennon's father, a merchant seaman during World War II, was often away from home and sent regular pay cheques to 9 Newcastle Road, Liverpool, where Lennon lived with his mother. The cheques stopped when Alfred Lennon went absent without leave in 1943. When he eventually came home in 1944, he offered to look after the family, but his wife (who was pregnant with another man's child) rejected the idea. Under considerable pressure, she handed the care of Lennon over to her sister after the latter registered a complaint with Liverpool's Social Services. In July 1946, Lennon's father visited Smith and took his son to Blackpool, secretly intending to emigrate to New Zealand with him. Lennon's mother followed them, and, after a heated argument, his father forced the five-year-old to choose between his parents. Lennon chose his father—twice. As his mother walked away, Lennon began to cry and followed her. Lennon then lost contact with his father for 20 years.

Throughout the rest of his childhood and adolescence, Lennon lived with his aunt and uncle, Mimi and George Smith, at Mendips, 251 Menlove Avenue, Woolton. In September 1980 he would have this to say about his childhood, his family and his rebellious nature:

The couple had no children of their own. His aunt bought him volumes of short stories, and his uncle, who was a dairyman at his family's farm, bought him a mouth organ and engaged him in solving crossword puzzles. Lennon's mother visited Mendips almost every day, and when he was 11 he often visited her at 1 Blomfield Road, Liverpool. She played him Elvis Presley records, and taught him to play the banjo. The first song he learned to play was Fats Domino's "Ain't That a Shame".

Lennon regularly visited his cousin Stanley Parkes in Fleetwood. Seven years Lennon's senior, Parkes frequently took him on trips, and the pair enjoyed films together at the local cinema. During the school holidays, Parkes often visited Lennon with Leila, another cousin, and they would all go to Blackpool on the tram two or three times a week to watch shows. They would visit the Blackpool Tower Circus and see artists such as Dickie Valentine, Arthur Askey, Max Bygraves and Joe Loss. Parkes recalls that Lennon particularly liked George Formby. They regularly passed Formby's house on the bus journey from Preston to Fleetwood, often spotting the singer and his wife sitting in deck chairs in their front garden and exchanging waves with them. Parkes and Lennon were keen fans of Fleetwood Flyers Speedway Club and Fleetwood Town FC. After Parkes's family moved to Scotland, the three cousins often spent their school holidays together there. Parkes recalled, "John, cousin Leila and I were very close. From Edinburgh we would bundle into the car and head up to the family croft at Durness. That went on from about the time John was nine years old until he was about 16".

Lennon was raised as an Anglican and attended Dovedale Primary School. From September 1952 to 1957, after passing his Eleven-Plus exam, he attended Quarry Bank High School in Liverpool, where he was known as a "happy-go-lucky" pupil, drawing comical cartoons and mimicking his teachers. At the end of his third year, his school report was damning: "Hopeless. Rather a clown in class. A shocking report. He is wasting other pupils' time." He was 14 when his uncle died in June 1955.

Lennon's mother bought him his first guitar in 1957, a cheap Gallotone Champion acoustic "guaranteed not to split". She arranged for it to be delivered to her own house, knowing that her sister, sceptical of Lennon's claim that he would be famous one day, hoped he would grow bored with music, often telling him, "The guitar's all very well, John, but you'll never make a living out of it". On 15 July 1958, when Lennon was 17, his mother, out walking near the Smiths' house, was struck by a car and killed.