The 75 year old becomes one of the oldest people to enter the competition.
The unnamed song is being written by Sacha Skarbek - who worked with James Blunt to compose his hit You're Beautiful.
The track will be recorded in London, Los Angeles and Nashville.
The last UKwin at the Eurovision Song Contest was in 1997 when Katrina and the Waves.
Humperdinck said: "It's an absolute honour to be representing my country for this year's Eurovision Song Contest….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."
This year's awards will be held in Azerbaijanin May.
Humperdinck’sprevious hit records include ‘Release Me’ and ‘The Last Waltz’.