He was born in Hamburg in Germany and studied at the School of Music there. A multi-instrumentalist, he was hired by Hans Busch to play with his orchestra before serving as a bandsman in the German navy during World War II. He later formed his own big band and toured with them and then worked as an arranger and producer, making hit records with Freddy Quinn and Ivo Robic. In 1961, he hired The Beatles to back Tony Sheridan on "My Bonnie Lies Over the Ocean", "When the Saints Go Marching In", "Ain't She Sweet" and "Cry for a Shadow," in a session for Polydor. These turned out to be the Beatles' first commercial recordings.
Kaempfert's own first hit with his orchestra had been in 1960 with "Wonderland by Night". Later commerical successes included "Tenderly", "A Swingin' Safari" and "Three O'Clock in the Morning".
Kaempfert penned a number of well known tunes which were hits for other artists. "Strangers in the Night" (with words by Charles Singleton and Eddie Snyder), originally recorded for the 1965 film A Man Could Get Killed, was a hit in 1966 for Frank Sinatra; "Wooden Heart", sung by Elvis Presley in the film GI Blues was a hit in 1961; and his instrumental "Moon Over Naples", when given words by Snyder, became "Spanish Eyes" (originally a hit for Al Martino and also recorded by Presley and many others).
By the 1970s, sales of Kaempfert's music had dropped off somewhat, but he continued to record (his version of the "Theme from Shaft" was admired by Isaac Hayes himself) and remained popular with audiences. He died unexpectly following a stroke at his home on Mallorca, shortly after a successful tour of Great Britain.