Jessie J was born Jessica Ellen Cornish in Redbridge, London, England. She attended Colin's Performing Arts School and as an eleven year old was cast in Andrew Lloyd Webber's West End production of Whistle Down the Wind.
Cornish has stated she was "never really that good at anything,." adding, "... Give me something to draw or an outfit to pick for someone, or hair, make-up, acting, write a song, I'm fine with it, but anything to do with sums – it was never my thing."
She also said she was always good at singing and it was her "thing." However, she got banished from the school choir, for being too loud. She stated "I was in it for a day and some of the adults were moaning that their kids were upset that I was too good. I was 11. Can you imagine? I was heartbroken."
At the age of 16 she began studying at the BRIT School, and joined an all girl group "Soul Deep." Jessie J has had an irregular heartbeat since the age of 11, and suffered a minor stroke at the age of 18. As a result, she doesn't drink alcohol or smoke. Having bad health has made her realize she couldn't take anything for granted and must look after her body.
She signed with Gut Records, recording an album for the label, but the company went bankrupt before releasing material. Jessie J then found success as a songwriter, gaining a Sony ATV publishing contract.
She was also the supporting singer for Cyndi Lauper during Lauper's UK dates of her 2008 Bring Ya To The Brink tour. Jessie began her career when she started to pen lyrics for the artists such as Chris Brown and Miley Cyrus. The biggest single she wrote was the Miley Cyrus song "Party in the U.S.A.."
Recording Jessie J's album Who You Are took six years, finally completed on January 19, 2011. In late 2010, Jessie J released her first single, "Do It Like a Dude." The single gained positive reception from critics. The single charted at number two on the UK Singles Charts, being held off the top-spot by Bruno Mars with "Grenade." In 2010, her single "Sexy Silk" was featured in the film Easy A.
Her follow-up single "Price Tag" was released in late January 2011. The single went straight to the top of the charts charting at number one. It remained at number one for two exclusive weeks, however was knocked off the top spot by school friend, Adele with "Someone Like You." "Price Tag" was released in the U.S. on February 1, 2011.
The single peaked at 23 on the Billboard Hot 100. It has since charted at number-one in New Zealand and Ireland. Her first American television appearance was as the musical guest on the 12 March 2011 episode of NBC's Saturday Night Live.
On February 25, 2011, her debut album, Who You Are, was released. Due to high demand and interest from fans for the album, the release date was pushed ahead by a month, from its original March 2011 release date. The album charted 6 March 2011 at number two on the UK Album Charts. In April 2011 the album debuted at number 11 in the U.S. and its single "Price Tag" was at 23. The video for the song featured singer B.o.B.
Jessie J went on tour as the opening act for fellow Capitol artist Katy Perry's California Dreams Tour in 2011.
Jessie J says she's bisexual.