[7] In 2015, Johnson auditioned for the twelfth series of The X Factor, singing American pop music family group The Jackson 5's "Who's Lovin' You".

[10] Johnson competed in the "girls" category at "bootcamp" and was mentored, at the decision of the public, by Rita Ora.

[8] She successfully made it past the six-chair challenge to "judges' houses", singing "And I Am Telling You I'm Not Going" by Jennifer Hudson; when Johnson arrived, all six chairs had been filled, and Ora described the atmosphere as "like a zoo".

[8] At judges' houses, she sang "Respect" by Aretha Franklin in front of Ora and American musician Meghan Trainor in Los Angeles;[8] this performance gained media attention, as Johnson wore two separate pairs of shoes, with some viewers inferring some sort of faking.

[11] Two weeks after that performance was recorded,[8] she was chosen by Ora for the live shows, along with Lauren Murray and Kiera Weathers; that category's Monica Michael later returned as a wildcard entry.

[12] Following the eliminations of Weathers in the second week, Michael in the third week and Murray in the semi-final, Johnson advanced to the final along with Reggie 'n' Bollie and Ché Chesterman singing a cover version of "I Believe I Can Fly" by R Kelly; additionally becoming the final female in the competition.

[21] The single dropped to number twelve the following week becoming the lowest ranking X Factor winner's song ever on the Christmas Day chart.

The song was a commercial success, reaching the top five in Scotland and the UK, and charting in many other European countries.

[25] In June, she performed "Tears" with Clean Bandit and a new version of the song "Over and Over Again" with Nathan Sykes at the Summertime Ball.

[31][25] In March 2018, Johnson released her fourth single, "Yes", a collaboration with the American rapper 2 Chainz, which peaked at number 65 in the UK.

[42] For the artwork of the single, Johnson posed completely nude, being photographed sitting down in front of a plain backdrop, with one leg raised towards her and the other one spread out.