Jessica Ellen Cornish (born 27 March 1988), known professionally as Jessie J, is an English singer and songwriter. After signing with Republic Records, Jessie J came to prominence with the release of her debut single, "Do It like a Dude", which peaked at number two on the UK Singles Chart. Her following single, "Price Tag", was an international success, topping the charts in nineteen countries, including the UK. It was followed by the release of her debut album, Who You Are (2011), which peaked at number two in the UK. Other singles from the album included "Nobody's Perfect", "Who You Are", "Domino" and "Laserlight", all of which peaked within the top ten in the UK, making Jessie J the first British female artist to have six top-ten singles from a sole studio album.

Jessie J's second album, Alive (2013), peaked within the top five on the UK Albums Chart and included the singles "Wild" and "It's My Party". The release of her third album, Sweet Talker (2014), was preceded by the single "Bang Bang" which debuted at number one in the UK and went multi-platinum worldwide. The album made the top five in the UK and peaked at number 10 on the US Billboard 200, her highest-charting album in the US. As of January 2015^[update], Jessie J had sold over 20 million singles and three million albums worldwide. In 2018, she released her four-part fourth album, R.O.S.E., followed by her Christmas album, This Christmas Day.

Citing various influences, Jessie J is recognised for an unconventional musical and performance style that mixes soul vocals with contemporary R&B, electropop, and hip-hop beats. She has received various accolades, including the 2011 Critics' Choice Brit Award and the BBC's Sound of 2011. Jessie J has supported various charitable causes, and has appeared on the UK charity telethons BBC Children in Need and Comic Relief. She has served as a coach on the television singing competition shows The Voice UK (2012–2013), The Voice Australia (2015–2016) and The Voice Kids UK (2019). In 2018, Jessie J won the sixth season of Singer, a Hunan TV competition show for professional singers.

Jessica Ellen Cornish was born on 27 March 1988 in Chadwell Heath in the London Borough of Redbridge, London, to Rose (née Archer) and Stephen Cornish. She was educated at Mayfield High School in LB Redbridge. This area was part of Essex until 1965 and Jessie J refers to herself as an Essex girl. She attended Colin's Performing Arts School and as an 11-year-old she was cast in Andrew Lloyd Webber's West End production of Whistle Down the Wind. She subsequently joined the National Youth Music Theatre and appeared in their 2002 production of The Late Sleepers.

Cornish has two elder sisters, who were both head girls at school. Unlike her academic sisters, Cornish has stated she was "never really that good at anything". She said, "At school they were like 'oh, you're a Cornish girl' and they kind of expected me to be the same as my sisters. 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 never based her intelligence on her exam results. She also said she was always good at singing and it was her "thing". In 2003, at age 15, she won Best Pop Singer in the TV show Britain's Brilliant Prodigies, performing as Jessica Cornish. At the age of 16 she began studying at the BRIT School and at 17 she joined a girl group named Soul Deep. She graduated in the class of 2006 along with singers Adele and Leona Lewis. She suffered a 'minor stroke at 18.' This was attributed to the heart condition Wolff–Parkinson–White syndrome, which she was diagnosed with aged 11.

Jessie J was signed to Gut Records, recording an album for the label, but the company went bankrupt before any material was released. She then found success as a songwriter, gaining a Sony ATV publishing contract. She was also the support act for Cyndi Lauper during Lauper's UK dates of her 2008 Bring Ya to the Brink tour (Lauper invited J to join her on stage for the performances of "Girls Just Want to Have Fun"). Jessie has also written lyrics for artists such as Chris Brown and Miley Cyrus, including "Party in the U.S.A.". Jessie J was also part of a girl band, called Soul Deep, for two years, however, believing "it wasn't going anywhere", she left the group. Despite people thinking that her first notoriety was through YouTube, Jessie was signed for four years before her first video was posted. Jessie first came to the attention of Lava Records when her publisher at Sony/ATV, Rich Christina, sent Lava president Jason Flom a link to her MySpace page, which the record executive loved. After seeing an impressive US showcase, Lava, along with several other labels, was keen to sign the artist but progress was hampered by her management's insistence on, what Flom called, a "crazy deal", and their refusal to let Jessie speak to any labels directly. Despite this, Senior Director of A&R at Lava, Harinder Rana, made surreptitious efforts to meet Jessie on her own in winter of 2008. Later in the year a change in management to Sarah Stennett and Nadia Khan of Crown Music allowed record deal negotiations to take place. Jessie eventually signed with Lava as part of a joint venture with Universal Republic.

Jessie J began recording her debut studio album in 2005 and it was completed on 19 January 2011. She revealed that "Big White Room" would be on the album and was written from an experience she had when she was aged 11, although she wrote the song at age 17, in the hospital, where a ward mate, a little boy, died. Jessie J says the album's title track, "Who You Are", is one of her proudest creations, she said the song is a "positive role model for young people" and "I always say that I'm half-artist, half-therapist". The song was written in 2005, when she just moved to Los Angeles, and was going through a very lonely difficult moment. A song called "Sexy Silk", which appears on the Easy A soundtrack, was originally going to be her first single. However, in late 2010 Jessie J released her first single, "Do It Like a Dude" which was co-written with George Astasio, Tj Normandin, Jason Pebworth, Jon Shave, Kyle Abrahams and Peter Ighile. Originally, she wrote the song with Rihanna in mind because "Rude Boy" was released at the time, partly inspiring the song. She then sent the song to her label, Island Records, before sending it to Rihanna's management. Island insisted the song become Jessie J's first single. The single gained positive reception from critics. The single charted at number two on the UK Singles Chart. Her follow-up single "Price Tag" was released in late January 2011. It was written by Jessie J, Dr. Luke, Claude Kelly, and B.o.B and peaked at number one on the UK Singles Chart. "Price Tag" was released in the US on 1 February 2011 and peaked at 23 on the Billboard Hot 100. "Price Tag" also charted at number-one in New Zealand and Ireland and is the most successful online video J has released. Her first American television appearance was as the musical guest on NBC's Saturday Night Live on 12 March 2011.

On 25 February 2011 her debut album, Who You Are, was released. The album first entered the UK Albums Chart on 6 March 2011 where it charted at number two. The album charted into the top ten in a number of countries and number 11 in the US. After the release she went on to release a third single from the album, "Nobody's Perfect". MTV reported that the single is, so far, only confirmed for release in the United Kingdom. The album's fourth single was "Who's Laughing Now". "Domino" was her second US single. The Dr. Luke-produced track was sent to mainstream radio on 6 September 2011. With the success of Who You Are in North America, Jessie was chosen to tour as the opening act for American pop artist Katy Perry's California Dreams Tour in 2011 but pulled out after breaking her foot in rehearsals. Jessie J served as the house artist at the 2011 MTV Video Music Awards, performing several of her original songs along with covers around commercial breaks.