The veteran singer will perform 'Love Will Set You Free' first on the night in Azerbaijan on May 26.
"I didn't know I was going to do it, the call came through and the BBC asked if I would do it," he told BBC Breakfast. "For them to have the confidence for me to represent the UK is wonderful."
When asked how long he took to decide to do the show, he said: "Two seconds. I jumped at it, I feel like I've won the lottery, it's unbelievable."
Talking about the song itself, he said: "It has a very English flavour to it, it's a waltz. I had 'The Last Waltz', which was a number one hit around the world. I'm hoping this waltz will waltz me to the top position.
"I'm not nervous about it, I've quite recently toured in Russia, Germany and France. I'm hoping to draw in some of those people. I hope they'll remember my name."
Humperdinck added that he will have plenty of time to rehearse the song before May 26.
"It's such a beautiful ballad. I'm going to be taking this back to the States when I tour. I'll know this song like the back of my hand. Everyday I'm singing it in my head."
Engelbert Humperdinck recently said that he was "gobsmacked" over the reaction to him representing the UK at Eurovision.
> Ten Things About... Engelbert Humperdinck
Watch the video for Engelbert Humperdinck's 'Love Will Set You Free' below: