The former Spice Girls singer – who is due to give birth to her first child with husband Stephen Belafonte in June or July – will be replacing radio DJ Kyle Sandilands on the panel for the talent search show.
With filming commencing just weeks after the 35-year-old star is due to give birth, Mel will be joining Boyzone star Ronan Keating and Australian singer Guy Sebastian in the hot seats.
She said: "I love Australia and can't wait to see all the amazing talent the country has to offer."
Meanwhile, the fourth and final judge – who will replace 'Torn' hitmaker Natalie Imbruglia – is yet to be announced, but it is widely rumoured former 'Neighbours' actress Natalie Bassingthwaighte will assume the role.
Mel – who also has two daughters, Phoenix, 12, and Angel, four, from previous relationships and is currently based in Los Angeles – recently hinted she would be taking over from Cheryl Cole on the UK version of the show.
The 35-year-old star said: "I think I might be coming over for quite some time at some point next year. Well, I'm not going by myself, am I? The whole family is going to move, I think.
"I don't think I was meant to say that though. Oh sorry, pregnant brain, maybe that was a secret."
Girls Aloud singer Cheryl is leaving her position on the British version to take a judging role on the upcoming US version along with show boss Simon Cowell.
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