A judge quotes lyrics from the rapper's hit Lose Yourself as she delivers a blow to the country's main conservative party.
A representative of the rapper confirmed to Variety magazine that he would donate the $600,000 payout he is due to receive after the court ruling on Wednesday.
The track used in the National Party advert was entitled "Eminem Esque" and licensed through an Australian production house.
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"The ruling clarifies and confirms the rights of artists and songwriters", Adam Simpson, the lawyer for Eight Mile Style told the publication.
The publisher had exclusive control over the song, and rarely gave permission for its use in advertising, the court said.
In his 132-day sentence, Cull says that "Eminem" as a copy sounds and copies reproduce, it is "lost". "You own it, you better never let it go".
Earlier this week, a report emerged about Em's publishing company winning big in its "Lose Yourself" copyright case against the New Zealand National Party. Its president Peter Goodfellow said: 'We purchased the music from a reputable Australian-based music production library, who had purchased it from a U.S. supplier'.