Lester was something of a child prodigy, and at 15 began studies at the University of Pennsylvania, where he first developed an interest in British film, particularly Ealing comedies.
In 1953, Lester moved to London and began work as a director in independent television. A shambolic variety show he produced caught the eye of Peter Sellers, who enlisted Lester's help in translating The Goon Show to television as Idiot Weekly. It was a hit, as were two follow-up shows A Show Called Fred and Son of Fred.
A short film Lester made with Spike Milligan and Peter Sellers - The Running, Jumping and Standing Still Film - was a favourite of The Beatles, and in particular John Lennon. When the band were contracted to make a film in 1964, they chose Lester from a list of possible directors. A Hard Day's Night showed an exaggerated and simplified version of The Beatles' characters, and proved to be an incredibly effective marketing tool. Many of its stylistic innovations survive today as the conventions of pop video, in particular the multi-angle filming of a live performance.