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The 37-year-old Australian presenter - who announced last month that he was quitting his Nova 969 breakfast slot after a decade - will be heard from 4pm until 6pm on weeknights in Sydney and Brisbane and from 6pm until 8pm in Melbourne and Adelaide.
Watts said in a statement: "I'm stoked to be doing drive at Triple M next year. Footy, rock and comedy is a trifecta of good times for me. Can't wait to start."
Southern Cross Austereo's head of content Craig Bruce added: "We're incredibly excited about Merrick joining us in 2012. He's the perfect choice for Triple M which is gathering momentum right around the country.
"Triple M will have rock, sport and comedy in spades for the drive home next year."
Watts revealed last year that a health scare with his baby son Wolfe made him reassess his career. "Wolfe was quite sick," he said. "It hit me for the first time that my job and career are so much less important to me than my son."
Watts used to host the Nova morning show with Tim Ross until Ross announced his departure in 2009.
Soon after, there were reports of jealousy and tension between the pair, but both denied the rumours and insisted that they love each other like "brothers".
Michael Wipfli and Ryan Fitzgerald have since been announced as Nova radio's new breakfast presenters.
> Tim Ross 'excited' about Merrick Watts quitting radio show
> Kyle Sandilands blasts Merrick Watts on radio
