Brucknell was born in Cheltenham, Gloucestershire, on 15 November 1984. She started singing at an early age, as well as playing the violin and the piano. Throughout her childhood, she took part in a number of charity concerts and musical theatre performances, and was a prolific award winner in the Cheltenham Competitive Festival. At the age of 11, she won a place in the National Children's Orchestra of Great Britain and continued touring with them annually. She was awarded music scholarships to Dean Close School, St. Edward's School and Clifton College in Bristol. She began touring internationally at the age of 16.

In 2003, Brucknell began writing and directing Interference, a science-fiction film. The film was accepted for the 2005 Cannes Film Festival. Following this, it was shown at the Portobello Film Festival in Palm Springs.

She revealed in an interview that the reason why she is not attempting to represent the UK is because the BBC felt it was a conflict of interest for a former X Factor contestant to be promoted by them given their involvement with the Eurovision and the fact that they already have their own singing contest, The Voice UK, although former X Factor contestant Andy Abraham represented the UK in 2008. In March 2015, Brucknell announced that she would release a Broadway album later in the year which would be recorded at Abbey Road Studios.

Before The X Factor, Brucknell worked as a Britney Spears, Christina Aguilera, and Lady Gaga tribute act. In June 2009, she appeared on Britney Spears Saved My Life, a documentary which aired on BBC Three.

In 2010, Brucknell contracted Guillain–Barré syndrome, a life-threatening muscle disorder, whilst singing in Corfu, which left her paralysed for four months.

In 2011, Brucknell auditioned for the eighth series of The X Factor. She sang "The Edge of Glory" for her first audition; all four judges (Gary Barlow, Kelly Rowland, Tulisa and Louis Walsh) voted to put her through to the "boot camp" stage of the competition. She performed "You Got the Love" and "Feeling Good" at boot camp, and made it through to judges' houses. Brucknell, who was 26 years old at the time, was put into the Over 25s category, which was mentored by Walsh. After performing "Beautiful Disaster", Walsh chose her to advance to the live shows.

Following the X Factor, Brucknell began teasing the release of her track "Red Shoes". Brucknell returned to The X Factor in 2013 when she performed alongside other former contestants such as Rylan Clark, Jedward, Wagner, 2 Shoes, Diva Fever and Johnny Robinson at the final in Wembley Arena. In January 2013, She went on her first tour which was dubbed the "Glamour and Damage" Tour. She performed "The Damage is Done" from her then forthcoming album Glamour and Damage. She featured on a single which was released in Germany entitled "No Tomorrow".

Are You On the List? A Guide on How to Become a Modern Socialite (co-author with Olivia Cox and Lewis-Duncan Weedon) (2014)

As of January 2016, Brucknell lives in Los Angeles.

Brucknell took the ESC News’ Track of the Year 2015 title with her Moldovan National Final entry “Yearning”, with 71% of the votes.