Walker, 18, was the favourite to win the grand final of the Network Ten singing contest and said he felt "blessed" to win.

"I just want to thank God, man. Hey, I want to thank my family for coming and supporting me. My family they came from New Zealand," he told the crowd on winning.

Walker, who was born in Melbourne, raised in New Zealand and is now a shop assistant in Coolangatta, Queensland, wins a $200,000 artist's development fund and a recording contract with Sony, with his single Black Box to be released soon.

Warner, 17, from Sydney, said she knew Walker would win.

"I have said all along he had it in the bag," Warner said.

Judges Ian "Dicko" Dickson, Marcia Hines and Jay Dee Springbett praised both contestants, saying it didn't matter who won because they would both have great careers.

Springbett said to Walker after performing: "You're Stan-bloody-tastic - you're a star in the making."

Dickson said: "Week after week you've stamped your individuality ... you're fantastic."

The grand final at the Sydney Opera House saw the top 12 reunite to perform.

The two finalists sang with Canadian star Michael Buble, performing his hit song Feeling Good as 6000 fans watched on in the sweltering heat.

Last year's Idol winner, Wes Carr, and singer Mika also performed.

Walker joins the ranks of previous winners including Carr, Guy Sebastian, Damien Leith and Casey Donovan.

He said he had imagined himself in the position of the original Australian Idol winner, Sebastian.

"I remember watching Guy, thinking one day I'm gonna be there."

This year's Idol has suffered a ratings drop, struggling to reach a million viewers each week, and there is some speculation it won't be back next year.

There were a number of changes this year as Springbett replaced judge Kyle Sandilands after he was fired for a scandal on his radio show, and the program also lost host James Mathison.