"We were really happy to have Keith as part of the inaugural Voice crew and of course he will always remain part of The Voice family in Australia," Michael Healy, Nine's Director of Television announced today.
"We are currently in negotiations with superstar musicians to fill the coaching roles in 2013."
"I've been so fortunate to have been a part of The Voice," Keith said a statement.
"And as much as I'd love to do it again, it's clear that the recording and promoting of a new album, a tour and other commitments, will keep me from being a part of the second season.
"To everyone who sang on the show, I thank you, you've inspired not just me, but countless others. To everyone behind the scenes, and to my on-camera family Darren, Delta, Joel and Seal, thank you for making it so much fun. Keep watching Australia!"
The 2013 line-up will be announced soon. There is no word yet on whether the other three coaches will return to the panel.
Keith, aka Mr Nicole Kidman, attracted popularity among viewers for his musical knowledge, genuine nature and incredibly shiny hair. His contestant Darren Percival landed runner-up to Seal's singer Karise Eden.
The news has sparked speculation about whether the 44-year-old country singer will join American Idol instead, and who his replacement will be on the high-rating talent show.
Keith addressed the rumour that he is joining American Idol at a Q&A with school students in Nashville last week, Billboard reports.
"I would love to do it and hopefully that happens," Keith said.
"I did get to do a similar role in Australia for The Voice, and I really enjoyed it. The thing about those shows is that mentoring aspect ... it's about passing it on."
The Hollywood Reporter reported that Keith is close to signing a contract worth between $3 million and $4 million for one season.
Keith would join confirmed judges Mariah Carey and Randy Jackson, and Nicki Minaj, who is reportedly in the process of wrapping up a deal.
So who should replace Keith on The Voice judging panel?
John Farnham would be our pick given he's "The Voice" from way back. We'd also love to see Olivia Newton-John or the remaining Bee Gee Barry Gibb imparting advice to singing hopefuls.
And what about Kylie Minogue? Her sister Dannii has found huge success as a judge on Australia's Got Talent and The X Factor UK. Should she be so lucky ... lucky, lucky, lucky?
Let's not rule out a country music replacement either Kasey Chambers, Adam Brand or Shannon Noll (remember Guy Sebastian became a judge on The X Factor)?
Jimmy Barnes would be a great choice too after his show-stopping performance on The Voice finale in June, singing with daughter Mahalia and her pal Prinnie Stevens, both contestants on the show.
In pics: The Voice around the world