Royal Academy of Music graduate SuRie will represent the UK at Eurovision 2018 with her track Storm.
SuRie - real name Susanna Cork - was announced as the winner of Eurovision You Decide after a live ceremony in Brighton, broadcast on BBC Two.
She was chosen via a combined public and jury vote, and said she would celebrate with "a bottle of something bubbly and a straw".
This year's Eurovision Song Contest will be held in Lisbon in May.
SuRie, from Bishop's Stortford, Hertfordshire, has previously appeared at Eurovision supporting two Belgian entries - as a backing dancer for Loic Nottet in 2015, and as musical director for Blanche in 2017.
As a child soloist, she performed for the Prince of Wales, and more recently provided backing vocals for Coldplay's Chris Martin, as well as Will Young.
Her song Storm was written by Nicole Blair, Gil Lewis and Sean Hargreaves.
Speaking ahead of the announcement, SuRie said: "My eyes were opened to the beauty of Eurovision a couple of years ago and I was working with the Belgians so false flagging for a different country but I had an amazing time.
"To be involved from my country, I'm a proud Brit... I'd love to be a part of Eurovision".
Last year's Eurovision was won by Portugal, with Salvador Sobral taking top honours with the ballad Amar Pelos Dois.
Lucie Jones, former X Factor contestant representing the UK with Never Give Up on You, came 15th after scoring 111 points.
The UK has won Eurovision five times but last triumphed in 1997 with Love Shine a Light, performed by Katrina and the Waves.