"I'm not quite sure what song yet ... it will be something off my last album (Madness) that I haven't released as a single," Sebastian said.
"I want it to be epic ... I just want it to represent us as a nation well. But also just be fun or be emotional."
The singer has been performing on a bigger stage recently during his arena tour and feels like a ballad is the way to go.
"I want to go huge with the screens," he added.
Kylie Minogue, Jessica Mauboy and even '90s punk band TISM (This is Serious Mum) were among the possible contenders, so it was no surprise the choice of Sebastian left some people disappointed.
Austrian drag performer Conchita Wurst won the 2014 Eurovision Song Contest.
Sebastion says he has no plans to follow in Wurst's footsteps and won't don a dress for his performance.
"It's very open, there's no real boundaries and that's what I love," the singer said.
Twitter debates raged over whether Sebastian was the right choice.
Others were more positive.
The selection of the inaugural Australian Idol winner even prompted tweets from abroad.
Read more: Disabled punk rockers to compete in Eurovision Song Contest
- AAP
