Emerick first started working as an assistant engineer at EMI at the age of 15. To familiarise him with his work, he was placed under the supervision of another assistant engineer, Richard Langham. On his second day of work at EMI, Langham was assigned to be the assistant engineer of Norman Smith, who would be doing the first recording session of the Beatles in the evening. As a new recruit, Emerick was not entitled to get over-time pay, but was lucky enough to witness the first-ever EMI recording session by the finalised line-up of the Beatles in 1962, during which the group recorded for the first time with new drummer Ringo Starr on what would eventually become their first hit single "Love Me Do". As assistant engineer, Emerick worked on numerous early recordings by the Beatles, and also helped record other artists for the label, including Judy Garland. He assisted at the EMI artist test of the Hollies. After working his way up to the position, Emerick engineered the 1966 number one UK Manfred Mann hit Pretty Flamingo.
Emerick took over as the Beatles' first engineer, when that spring Smith became a producer, at the request of producer George Martin. Emerick's first album with the Beatles as chief engineer (under producer Martin) was Revolver. "Tomorrow Never Knows" was the first track recorded for the sessions and first that he worked on. It was Emerick's innovation to record John Lennon's vocal through a Leslie speaker on the song, to get the ethereal sound Lennon wanted. In 1967, Emerick engineered "Being for the Benefit of Mr. Kite!", one of the most musically complex songs on Sgt. Pepper's Lonely Hearts Club Band. Lennon told Martin he wanted to re-create the "carnival atmosphere" of the Pablo Fanque circus poster that inspired the song. For the Middle eight bars, Emerick spliced together multiple recordings of fairground organs and calliope in an attempt to create the effect; after a great deal of unsuccessful experimentation, Martin instructed Emerick to chop the tape into pieces with scissors, throw them up in the air, and re-assemble them at random.
Emerick abandoned work on The Beatles on 16 July 1968, fed up with the tensions and arguments that hampered the sessions. He returned to work with the Beatles on Abbey Road.
Emerick received Grammy Awards for the engineering of Sgt. Pepper's Lonely Hearts Club Band and Abbey Road.
Despite his departure from the "White Album" sessions, Emerick remained on good terms with the Beatles, particularly Paul McCartney, who invited Emerick to quit EMI and come and work for their company, Apple Corps Ltd., in 1969. In addition to engineering duties, Emerick would oversee the building of the Apple recording studio.
His post-Beatles career included work with Paul McCartney (including Band on the Run, which netted Emerick another Grammy, London Town, and Flaming Pie), Elvis Costello (for whom he produced Imperial Bedroom and All This Useless Beauty), Badfinger, Art Garfunkel, America, Gino Vannelli, Supertramp, Cheap Trick, Nazareth, Chris Bell, Split Enz, Trevor Rabin, Nick Heyward, Big Country, Gentle Giant, Mahavishnu Orchestra, Ultravox, Matthew Fisher's first solo album Journey's End, Kate Bush's demo tape to EMI, which landed her a record deal, and Jeff Beck, as well as Nellie McKay's critically acclaimed 2004 debut CD Get Away from Me.
He was the sound engineer on Robin Trower's album Bridge of Sighs, and credited by both Trower and producer Matthew Fisher for that album's acclaimed sound. He also recorded the debut album for Stealers Wheel, featuring the single "Stuck in the Middle With You" as well as The Zombies famed Odessey and Oracle album featuring "Time of the Season".
In 2003, he received his fourth Grammy, a Special Merit/Technical Grammy Award.
In 2006, Emerick released his memoir, Here, There, and Everywhere: My Life Recording the Music of The Beatles (Gotham Books, ISBN 1-59240-179-1), co-authored by veteran music journalist Howard Massey.
On 3 April 2007, it was announced that Emerick would be in charge of a re-recording of Sgt. Pepper's Lonely Hearts Club Band by contemporary artists, including Oasis, The Killers, Travis and Razorlight. Emerick used the original equipment to record the new versions of the songs, and the results were broadcast on BBC Radio 2 on 2 June 2007, marking the album's 40th anniversary.
Emerick now resides in Los Angeles.