Donovan was the youngest person to win the Australian Idol competition. She won the competition at 16 while still a student at the Australian Institute of Music in Sydney, Australia. She comes from a family of musicians, with several of her relatives pursuing musical careers, including her father, a member of indigenous country band The Donovans.

While Donovan performed well throughout the Australian Idol competition, receiving effusive praise from all three judges, she was not widely considered a favourite to win. During the competition, she received some outside success, winning the Most Promising New Talent Award at the 2004 The Deadlys, which honor indigenous talent in Australia. Nevertheless, she surprised many by first making it to the final at the expense of Courtney Murphy, and then defeating widespread favourite Anthony Callea in the final. Her first single, "Listen With Your Heart" was released digitally on November 21, 2004 and officially in stores on November 29, 2004. It debuted at #1 on the ARIAnet singles chart, while her album For You debuted at #2 on the album charts. Her second single "What's Going On?" debuted in the top 20 in February 2005. Her third single "Flow" was withdrawn from release in July 2005 when radio stations failed to play it, and after the album had dropped out of the album charts.

In just 12 months and now just 17 years of age, Casey has won Australian Idol, three Deadly awards (Most Promising New Talent 2004, best album and best single 2005), received two ARIA nominations (best album, best single), had a #1 debut single and #2 debut album, and holds the record for fastest download of a single on Telstra's Bigpond. While Callea has been afforded more support, Casey has been busy building her fan base with small intimate gigs at venues such as The Basement (with Wendy Matthews) and The Vanguard, as well as a residency at the Sandringham Hotel. She recently was invited to Brisbane to perform at the Foxtel 10th Birthday Party and to Melbourne for her first gig in that state held at the Grand Central receiving rave reviews. Casey has spent much of the time this year writing, as well as collaborating with respected Australian song-writers, new material for her next album which is due for release mid 2006.

On March 26 2006, she performed at the Closing Ceremony for the 2006 Melbourne Commonwealth Games.