It was an underdog victory for rapper Marcus Gray, a relatively obscure artist once known as Flame whose five-year-old lawsuit survived constant court challenges and a trial against top-flight lawyers for Perry and the five other music-industry heavyweights who wrote her song.
The amount was less than the nearly 20 million dollars (£16.5 million) sought by lawyers for Gray and his two co-writers on the 2009 song Joyful Noise, but they said they were pleased with the decision.
"These defendants have made millions and millions of dollars from their infringement of the plaintiff's copyright," Gray's lawyer Michael A Kahn told the jury.
Perry herself was hit for just over 550,000 dollars (£457,000), with Capitol Records responsible for the vast majority of the money.
Defence lawyers had argued for an award of about 360,000 dollars (£297,000) after the jury decided earlier this week that Dark Horse copied Joyful Noise.
Perry's lawyer Christine Lepera said they planned to vigorously fight the decision.
"The writers of Dark Horse consider this a travesty of justice," she said.
Both sides agree that Perry herself made a profit of 2.4 million dollars (£2 million), while Gray's lawyers argued that her song had grossed about 41 million dollars (£34 million). The pop star testified at the beginning of the trial but has not been in court since.
Because the rhythmic instrumental riff from Joyful Noise plays through 45% of Dark Horse, Mr Kahn said his clients were entitled to 45% of the entire earnings of Perry's album Prism, where her song appears.
The defence recommended dividing the award money by the number of songs on the album.
"A CD is a CD, you can't break it into pieces," Mr Kahn said. "Every album had an infringing song. And not just any song, but the most popular song on the album."
Both sides agreed that sales and streams of Dark Horse should be in play.
Lawyers for Perry and her co-defendants, which included Capitol Records and producer Dr Luke, said the millions Gray sought were based on ludicrous figures.
"They're not seeking fairness," the defendants' lawyer Aaron M Wais told the jury. "They're seeking to obtain as much money as possible."
Mr Wais argued, based on expert testimony, that the disputed part of Dark Horse was worth only 5% of its earnings.
He argued that the biggest driver of the song's earnings were not any part of the song itself, but the celebrity of Perry, who was already a major star when she recorded the song.
"The reason why people buy a Katy Perry album, buy a Katy Perry song, is because it's Katy Perry," he told the jurors. "If you replaced her with an anonymous artist, do you really think it would sell as well?"
At the end of the first phase of the trial on Monday, jurors surprised many by finding all six writers of Dark Horse were liable for copying from Joyful Noise, though only a section of the instrumental track was in dispute.
That included Perry, who only co-wrote the lyrics to the song, and Juicy J, who only provided a rap break for it.
All the songwriters testified that they had never heard of Gray or his song before he and co-writers Emanuel Lambert and Chike Ojukwu sued five years ago.
But Gray and his lawyer only had to prove that they had ample opportunity to have heard it.
Recent years have brought similar wins in disputes over hit songs, though usually with big pop stars on both sides.
In the case of another 2013 mega-hit, Blurred Lines, a jury found singers Robin Thicke and Pharrell Williams copied R&B legend Marvin Gaye's Got to Give it Up. Thicke and Williams were ordered to pay Gaye's children nearly 7.4 million dollars (£6 million). The award was trimmed last year to just short of 5 million dollars (£4.1 million) on appeal.
No fight was required in 2016 when Tom Petty won a piece of British soul singer Sam Smith's hit Stay With Me. Petty's publishers said that while it was likely coincidental, the song's melody closely resembled Petty's 1989 song I Won't Back Down. Petty and Jeff Lynne were added as co-writers on Smith's song, but details on a dollar figure were not released.
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