Ke$ha
Her song Tik Tok launched her on to the international music stage, but before she had a No.1 song Ke$ha was better known for singing back up on tracks for artists such as Britney Spears (Lace and Leather) and Flo Rida (Right Round). She was also an established songwriter, co-writing songs for The Veronicas, Kelly Clarkson, Miley Cyrus and Ariana Grande.
Emeli Sande

Singer-songwriter Ke$ha who had a huge hit with Tik Tok. Source: Supplied
UK singer-songwriter Emeli Sande is a stape in the British music industry and one of the most recognisable voices in the world, but before she hit the big time with Read All About It she was synonymous with a range of popular rappers. She appeared singing vocals on Chipmunk’s debut single Diamond Rings, which she also wrote, but when the video was released she was shocked to see she had been replaced with someone else miming over her vocals. Sande had the last laugh, however, going on to have huge success as a solo artist and continuing a run writing songs for names such as Alicia Keys, Leona Lewis, Susan Boyle and Katy Perry.
Katy Perry

My Kind Of Love singer-songwriter Emeli Sande. Source: Supplied
Long before she kissed a girl and liked it, Katy Perry got her start as a Christian singer-songwriter under her birth name Katy Hudson. This included a stint singing back-up vocals for Christian alt metal band P.O.D (of Alive and Youth Of The Nation fame) in the early noughts on their track Goodbye For Now.
Connie Mitchell
As the frontwoman for Aussie electro pop group Sneaky Sound System, Connie Mitchell is more famous for hits like I Love It, UFO and Pictures. However, she has also had a hugely successful collaboration with Kanye West, singing back-up on four tracks from his acclaimed album Graduation (including Flashing Lights and Can’t Tell Me Nothing). She has also sung on songs from Snoop Dogg and Rick Ross.
Mariah Carey

Connie Mitchell from Sneaky Sound System. Source: Supplied
Before she went on to become the most successful female singer of all time with more than 63 million albums sold and 18 number one singles (she’s currently tied with Elvis for the most ever for a solo artist), Mariah Carey was a struggling teenager in New York City trying to get a break. That came in the form of singing back-up for Brenda Star in the eighties – who became one of her closest friends - before this eventually brought her to the attention of executives at Sony who soon gave her a record deal.