The former Tasmanian, who made a name for himself on Australian Idol in 2009, is supporting Mariah Carey at A Day on the Green in Queensland.

Barnes admits he is excited and nervous for the Sirromet Winery gig, but he is also disappointed that he missed his 20 year Ulverstone High School reunion because of it.

"I was meant to be there," he said of the reunion that was on this weekend.

"I was really looking forward to coming down, but I'm hoping I'll be down early next year instead."

This isn't the first time Barnes has played at A Day on the Green.

He opened for Bryan Adams nine years ago.

"The day there went really, really well and I got a good response from the crowd," Barnes said.

"The promoter said stay in touch with me and if we get another opportunity to put you forward, we'll put you on another one."

He did get the chance the same yearhe was on Australian Idol, but due to the reality show's contracts, he was unable to do both.

Barnes said he didn't tell anyone he had applied to support Carey, because he didn't want to jinx it.

"I was sitting at my computer a couple of weeks ago and the email came through saying 'Congratulations you've got the spot'," he said.

"It was pretty awesome.

"This will be the biggest gig of my life."

Barnes and his six-piece band will play a number of tracks off his full-length album Jet Trails and his recent EP Flesh & Bone.

He has recently released a new single called Waiting on the Day.

However, Barnes said he would wait to see the mood of the crowd before deciding whether to play the new song.

The song is a tribute to every parent who has endured the loss of a child, and is also for Barnes and his wife's baby Grace, who they lost two years ago.

Following today's gig, Barnes will release another song early next year and hopes to go back to Nashville to record in the near future.