Pop star Katy Perry has lost, for the second time, her years-long trademark case against an Australian fashion brand called Katie Perry.

In a High Court ruling on Wednesday, judges found that designer Katie Taylor had not hurt the US singer's reputation or caused confusion with her clothing brand, which started in 2007.

Taylor, who changed her surname in 2015, successfully sued Perry two years ago for selling merchandise during a 2014 Australian tour, but the ruling was overturned in 2024, with the designer's trademark cancelled.

The new decision found that Perry's reputation was so well-established in Australia that anyone seeing Taylor's clothing brand would not confuse the two names.

"This has been an incredibly long and difficult journey," Taylor said in a statement shortly after the decision.

"But today confirms what I always believed - that trademarks should protect businesses of all sizes."

The case centres around the sale of clothes under the Katie Perry brand in Australia and the sale of Katy Perry-branded merchandise during the singer's tour.

In 2007, Taylor - who went under her maiden name at the time - registered her business name, Katie Perry, and applied for a trademark.

Since 2008, she has sold clothes at local markets, has a website, and maintains several social media accounts under the Katie Perry brand.

But in 2009, lawyers for the Roar singer asked Taylor to stop using her brand and signalled plans to oppose a trademark application, but later dropped legal action.

"I had never heard of the singer when I started my label," Taylor said, with court documents detailing how she first heard of Katy Perry in mid-2008 when the song I Kissed A Girl came on the radio.

"I was simply building a fashion business under the name I was born with."

In 2023, Taylor sued the singer for trademark infringement and won, with the singer's sale of jackets, hoodies, T-shirts and sweatpants during a 2014 tour in breach of trademark laws.

But in 2024, it was overturned on appeal, with judges saying Perry had been using her name as a trademark five years before Taylor started her business.

At the time, Taylor described the case as a "David and Goliath" battle, saying she was devastated by the decision.

On Wednesday, the High Court - in a majority decision - found that given the "heightened strength of the reputation of Katy Perry", that "no ordinary person in Australia... after a moment's reflection" would think Katie Perry products were linked to the US singer.

"This case has never just been about a name," Taylor said.

"It has been about protecting small businesses in Australia, for standing up for what is right and showing that we all matter."

In recent years, Katy Perry has made headlines for a range of reasons, from being mocked for kissing the earth after disembarking a Blue Origin spaceflight to her high-profile divorce from actor Orlando Bloom and her new relationship with former Canadian Prime Minister Justin Trudeau.