Isaiah auditioned for the eighth season of The X Factor Australia, singing a cover of Adele's "Hello". Making it through to Bootcamp, he performed a cover of Alicia Keys' "If I Ain't Got You". From the live shows, he advanced to the Grand Final.[4]
On 21 November 2016, at the Grand Final, Isaiah performed Avicii's "Wake Me Up" with Jessica Mauboy, and his winner's single "It's Gotta Be You", winning the contest. His winner's single peaked at number 26 on the Australian Singles Chart. The song also charted in Denmark, Netherlands, New Zealand, and Sweden.[5]
On 9 December 2016, Isaiah released his debut studio album Isaiah. The album peaked at number 12 on the Australian Albums Chart.[5]
On 9 May 2017, he qualified from the first semi-final and competed in the final on 13 May, finishing in 9th place.
Throughout 2019, Firebrace completed a 55-date 'Spirit and Beyond' tour through central and regional Australia, where he made it a priority to speak with as many Aboriginal school children as possible to pass on powerful messages about working hard to achieve goals and the importance of finding a passion.[7]
In 2019, Firebrace sang the Australian National Anthem at the TAB Million Dollar Chase greyhound race[8] at Wentworth Park.
In July 2020, Firebrace released "Know Me Better". He said "This song actually means a lot to me because I finally feel like I'm starting to know myself better and I am heading in the direction I want to with my music. I've been in the studio a lot over the last three years and have experimented with lots of styles but 'Know Me Better' is a song that I'm really proud to release. I love the song, I love the production and I just can't wait to be able to show people this song".[7] Firebrace also announced that he was writing a children's book, "The Purple Platypus", which pushes a positive message for kids who feel different.[7]
In 2022, Firebrace participated in Eurovision - Australia Decides for a chance to represent his country in the 2022 contest. He duetted with singer Evie Irie with the song "When I'm With You", ultimately finishing in 10th place.
In September 2022, Firebrace released "Come Together" with Lee Kernaghan and Mitch Tambo.[10] The song coincides with Firebrace's new children's book, also called Come Together, published on 16 November 2022.[10][11] Illustrated by Jaelyn Biumaiwai, the book was shortlisted for the 2023 CBCAEve Pownall Award.[12]
In November 2022, Firebrace released the self-composed Christmas song "First Christmas".[13]