The Beatles' first contract with manager Brian Epstein is expected to sell for about £300,000 at auction.
Paul McCartney, John Lennon, George Harrison and their first drummer Pete Best signed the document on 24 January 1962, before achieving worldwide fame.
"[Epstein] stopped them eating on stage," Gabriel Heaton, a specialist at the Sotheby's auction house, said.
"He made sure they played the songs properly and coherently, and he got them bowing at the end of a set."
The document, said to have been signed by the band in the front room of Best's mother's house, was the first of two contracts drawn up between Epstein and The Beatles.
It gave Epstein responsibility for finding the band work, and managing their schedule and publicity.
He was also to oversee "all matters concerning clothes, make-up and the presentation and construction of the artists' acts and also on all music to be performed".
Mr Heaton said: "He was just blown away by the passion, the energy, the charisma, the raw sexuality on stage.
"They had the stage energy but he instilled a sense of professionalism in them."
The band's previous manager, Allan Williams, had warned Epstein "they'll let you down".
- The Liverpool-born manager was in charge of the record section of his family's shop, North End Music Stores, when he first saw The Beatles at the city's Cavern Club
- After signing the band, he changed their image from leather jackets and jeans to suit and ties
- Epstein managed other Merseyside acts, including Cilla Black, and Gerry and The Pacemakers
- He died in 1967, aged 32, following a drug overdose - the inquest ruled it as an accidental death
However, Epstein did not sign the contract himself, saying "even though I knew I would keep the contract in every clause, I had not 100% faith in myself to help The Beatles adequately".
"I wanted to free The Beatles of their obligations if I felt they would be better off," he said.
The contract outlines that Epstein's fee would be 10%, rising to 15% if their earnings should exceed £120 a week - McCartney had negotiated the maximum limit down from 20%.
Following Best's departure from the band, another contract was signed on 1 October 1962 with Ringo Starr as drummer - and Epstein's cut at a higher percentage.
The original contract, from the collection of Epstein's publisher Ernest Hecht, is being auctioned for the first time next month.