[4] Sebastian has worked with a number of notable American musicians, including Brian McKnight, Robin Thicke, Steve Cropper, John Mayer, Jordin Sparks, Eve and Lupe Fiasco.

"Battle Scars", a collaboration with Fiasco, spent 20 weeks on the US Billboard Hot 100 chart, peaking at number 71 and achieved platinum certification.

[15] Sebastian has reached the top ten in New Zealand with an album and six singles, including two number ones, and gained six platinum and three gold certifications there.

Sebastian has sung at many notable events, including performing for Pope Benedict XVI, Oprah Winfrey and Queen Elizabeth II.

"[30][31] Sebastian was made a Member of the Order of Australia (AM) in the 2019 Queen's Birthday Honours in recognition of his significant service to music and charity.

[40] As a child, Sebastian took violin lessons; he would later learn to play guitar, drums and piano, although he has had no formal training in these other musical instruments.

He taught vocals at Temple Christian College and other high schools while also working as a recording engineer and studying music technology at the University of Adelaide's Elder Conservatorium.

He progressed through the Idol series, establishing a strong fanbase and praise from the judges, who often made reference to his afro hairstyle which became a focal point of his image.

[53] Beautiful Life, Sebastian's second album, had a more R&B edge to it and included songs he co-wrote with Robin Thicke and Brian McKnight and "Forever with You", a duet with American R&B singer Mýa.

[59] Sebastian performed at the 20th Anniversary SAFM Sky Show in Adelaide in front of approximately 150,000 people along with Slinkee Minx, one of the largest open-air concerts held in Australia in 2005.

[70][71] In early 2007 it had been announced Sebastian would be recording a tribute album of soul classics in Memphis, Tennessee, with Stax musicians who played on and wrote some of the original songs.

[72] Sebastian wrote about his time in Memphis in a series of blogs for Australian newspapers, "I started recording four days ago with the band members from Booker T and the MGs.

Sebastian was given Groups in 2010, and was assisted in choosing his final three acts by Rai Thistlethwayte, lead singer of Thirsty Merc, Snoop Dogg and Usher.

[122] In November 2011 "Don't Worry Be Happy", a pop song Sebastian wrote after encountering an angry motorist in Los Angeles, was released as the lead single of his seventh album Armageddon.

[130][131] He came to Australia in mid September to promote the single and the release of his album, and he and Sebastian performed "Battle Scars" live for the first time on The X Factor.

[142] The fourth single "Get Along", a song about the harm caused by religious, cultural and racial intolerance reached number five and triple platinum certification.

[171] Sebastian was made a Member of the Order of Australia (AM) in the 2019 Queen's Birthday Honours in recognition of his "significant service to the music industry and charitable initiatives".

[174] He received 2019 ARIA Award nominations for Best Male Artist and Best Pop Release, and won for Best Video and Song of the Year for "Choir".

[177] Sebastian cites a number of musicians as his musical influences, including Sam Cooke, Otis Redding, Donny Hathaway, Stevie Wonder, Chicago, and Boyz II Men.

In an article in The Daily Telegraph, Kathy McCabe said of his songwriting skills, "Sebastian has matured into a genuine hitmaker, his gift with melody so finely-honed he can pretty much punch out a catchy number in his sleep.

"[185] Jamie Horne wrote in The Border Mail, "The inaugural winner's longevity [...] can be attributed to the fact that he's an accomplished musician and songwriter" and AllMusic reviewer Jon O'Brien said, "it's a testament to his vocal abilities and songwriting skills that, unlike many of his fellow winners, he's remained popular enough to see out his rather ambitious Sony contract [...] a subtle and natural progression with each album, explains why he's managed to survive once the show's publicity machine died down.

"[186][187] In 2008 "Receive the Power", a gospel song written by Sebastian and Gary Pinto, was chosen as the official anthem for the Roman Catholic Church's XXIII World Youth Day.

[200] He produced a song called "Think of Me" for 2009 Australian Idol Stan Walker's debut album, as well as playing most of the musical instruments on the track.

The invitation only event was attended by the film's director Kenny Ortega and Jackson's brother Jackie Jackson[210] Oprah Winfrey's official welcome to Sydney and wrap up party, December 2010: Sebastian was the guest performer at an event at Sydney's Botanical Gardens to officially welcome Oprah Winfrey and her American audience members to Australia.

He performed at The Black Eyed Peas Peapod Benefit Concert which was attended by musicians, DJ's, philanthropists, Hollywood celebrities and industry executives.

Their 2011 jam session was hosted by Jimmy Fallon and other performers included Sara Bareilles, Lalah Hathaway, Booker T. Jones and Chaka Khan.

[233] Sebastian is also strongly committed to the Sony Foundation, which raises funds to help young Australians facing homelessness, severe illness, disability and isolation.

In 2005 he was the guest performer on the annual Indian Pacific Outback Christmas Journey which raises money for the Royal Flying Doctor's Service.

[239] Sebastian regularly performs at other fundraising events including Brisbane radio station B105's Christmas appeal for the Royal Children's Hospital,[240] and Perth's annual Telethon.

[247] Sebastian was an ambassador for the 2020 MEN-tality project for Beyond Blue shot by Peter Brew-Bevan, alongside Osher Gunsberg, Rodger Corser and Andrew Tierney.