The National Party's use of the track 'Eminem Esque' breached copyright, the High Court has ruled.
Eminem's music publisher Eight Mile Style sued the National Party and others for breaching copyright by using music similar to his song 'Lose Yourself' in its advertising during the 2014 election campaign.
The ad featured rowers powering through the water against the background of a guitar riff, which Eight Mile Style said was copied off the opening bars of the song.
The court has ruled that the song was covered by copyright, and that the track used by National was a copy of 'Lose Yourself'.
Read the full judgement here
Eight Mile's lawyer Garry Williams had argued that 'Lose Yourself' was without a doubt the crown jewel in Eminem's catalogue, and it was extremely valuable.
Lawyers for the National Party had argued the work had "a low degree of originality" and that parts of it were unoriginal.
They described the music as library music and said it had been purchased from production music supplies company Beatbox, which is based in Australia and Singapore.
The court ruled today that Eight Mile Style was entitled to damages of $600,000 with interest from 28 June 2014.
It said the differences between the two works were "minimal".
"The close similarities and the indiscernible differences in drum beat, the 'melodic line' and the piano figures, make 'Eminem Esque' strikingly similar to 'Lose Yourself'".
The court ruling said although copyright infringement did occur, the National Party's actions were taken after receiving advice and no additional damages were awarded.
The damages were the equivalent to what it would have cost to use the track if permission had been granted, the court judgement said.
The ad was played over 11 days with 186 TV viewings and was also uploaded onto the internet.
The three-week trial was held in the High Court in Wellington in May.
The National Party said it was disappointed with the ruling.
Its president, Peter Goodfellow, said the party took extensive advice before using the track.
He said it has a legal claim against the suppliers and licensors of the song.
National 'naive' - copyright expert
James and Wells senior associate and copyright lawyer Ben Cain told The Panel he thought the National Party was "naive" and the similarities between the songs should have set off alarm bells.
"I think anybody and everybody that heard that music thought 'oh, that sounds a bit too similar'," Mr Cain said.
"And [National Party campaign manager] Steven Joyce, with his background in radio, he should have been alive to the possible issues."
He said the National Party was always facing an uphill battle to show they had not infringed on copyright.