Ryan began writing songs for artists such as Oh Honey, rapper Skizzy Mars and Bea Miller before releasing music of her own. In 2014, she was featured on DJ duo Tritonal's single, "Now or Never", and in 2015, she released her first song as an artist, "Ignition/Do You", a mashup of "Ignition" and "Do You". Her first two original singles, "Mine" and "Dead", followed shortly thereafter.

In 2015, Ryan inked a deal with Columbia Records, with whom she released her debut EP entitled Mine. Her songs have received praise from music bloggers and artists alike, with Tove Lo praising "Mine" as "GOLD", Taylor Swift including the song on a handwritten list titled "New Songs That Will Make Your Life More Awesome (I promise!)", The Fader describing it as "excellent", and Billboard calling Ryan's voice "magnetic". In 2015, Nylon called Ryan a pop singer "primed for stardom".

On March 4, 2016, Ryan released "Chronic", an electropop song that serves as the lead single from her forthcoming debut album. The music video was released in April. "Boyz N Poizn" was released as the second single on May 5, 2016, with its music video released in June.

Bea Miller's song "Young Blood", co-written by Ryan, peaked at number 4 on the Billboard Dance Club Songs and number 40 on the Billboard Mainstream Top 40. It received a Radio Disney Music Award for "Best Song to Rock Out to With your BFFs".

On September 29, 2016, Ryan released the song "All We Know", as part of a collaboration with The Chainsmokers. The song peaked at number 18 on the US Billboard Hot 100, and at number 24 on the UK Singles Chart. On February 3, 2017, she released the third single off her upcoming album, entitled "Dark Side".