The 75-year-old housewives' favourite will perform at the show in Azerbaijan in May.
He said in a statement: "It's an absolute honour to be representing my country for this year's Eurovision Song Contest.
"When the BBC approached me, it just felt right for me to be a part of an institution like Eurovision. I'm excited and raring to go and want the nation to get behind me!"
Humperdinck last had a UK hit in 1972 with the song Too Beautiful to Last, but he has a quality-filled team behind his efforts. Writers include Ivor Novello Award-winning Sacha Skarbek, and the producer is Martin Terefe, whose previous talents include Mary J Blige and James Morrison.
A rep for the BBC, which airs the contest, says: "Not since the '70s have we had such an established international musical legend represent the nation. We couldn't be more delighted.
"Engelbert's experience leaves us in no doubt that he will be able to deliver a standout performance in front of 120m viewers worldwide."
Sir Cliff Richard, Sandie Shaw, Olivia Newton-John and Lulu have all represented the UK in the past. Katrina & The Waves gave the nation its last Eurovision win in 1997.
Last year saw a sustained campaign by established popsters Blue to take the Eurovision crown but, despite an intense composition, production and popularity campaign, the boy band only managed 14th position with their song I Can, trumped by Ireland's own poptastic twins Jedward, who came in at number 6 with the song Lipstick.
Humperdinck faces some tough competition this year - Julie Frost, the woman who teamed up with Madonna to write Golden Globe-winning track Masterpiece for the film W.E., is the brains behind love song Best Thing I Got, which Aya hopes to take to the European music competition as Denmark's representative.
At least he won't have to deal with fellow crooner David Hasselhoff - the former Baywatch star dismissed reports he would be representing the Netherlands at the Eurovision Song Contest last year.
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