Previous winners of the prize honoring up-and-coming artists on the British pop scene were Ellie Goulding, Florence and the Machine and Adele.
"This is epic! It has been a dream since I was a little girl to win a BRIT. I can't believe it's happened!" said Jessie, whose real name is Jessica Cornish.
The 22-year-old from Essex has written several songs for established stars including Miley Cyrus and Christina Aguilera.
Her single "Do It Like a Dude" was released by her Island Records label, part of Universal Music.
The 2011 BRIT awards, Britain's top pop honors, will take place on February 15 at London's O2 Arena. Take That and Plan B have been confirmed to perform at the show.
Source: The News