Swift's text was accompanied by a photo of her with a cat. Her "Childless Cat Lady" comment was a nod to remarks made in 2021 by Vance, who is Trump's candidate for vice-president.

Vance, the Ohio senator, has faced a backlash for a clip in which he called several prominent Democrats - including Harris - "a bunch of childless cat ladies who are miserable at their own lives". He recently said his comments were "sarcastic".

Swift went on to compliment Harris's choice of vice-presidential candidate, Minnesota Governor Tim Walz, who she said had been "been standing up for LGBTQ+ rights, IVF, and a woman's right to her own body for decades".

The singer said she was in part motivated to share her voting decision with the public after an AI image of her falsely endorsing Trump was posted on his website.

"It really conjured up my fears around AI, and the dangers of spreading misinformation," she said. "It brought me to the conclusion that I need to be very transparent about my actual plans for this election as a voter."

Swift is one of several celebrities to endorse Harris, including singers John Legend and Olivia Rodrigo, actor George Clooney and director Spike Lee.

Meanwhile, former wrestler Hulk Hogan, TV star Amber Rose and billionaire Elon Musk have endorsed Trump.

Swift's intervention came after a fiery 90-minute presidential debate, during which the two candidates sparred over issues such as abortion rights, the economy and immigration.

It is not the first time the pop star has endorsed the Democratic nominee in a race against Trump. Swift announced her support for President Joe Biden and Harris as his vice-president a month before the 2020 election.

Swift was also a vocal critic of Trump during his presidency surrounding the nationwide protests over the police murder of George Floyd.

"After stoking the fires of white supremacy and racism your entire presidency, you have the nerve to feign moral superiority before threatening violence?" she posted on Twitter/X. "We will vote you out in November."

Noting Swift's political past, one academic who studies the intersection of media and politics suggested that the endorsement was unlikely to move the needle in Harris's favour.

"No surprise at all, she endorsed Biden and Harris in 2020 so we already knew her politics," said Lauren Rosewarne, a University of Melbourne professor.

Swift's endorsement could impact on voter registration, Ms Rosewarne told the BBC. But because her fan-base skews young and female - and that is already the Harris supporter base - her endorsement may not have a big impact come November.

The singer has 283 million followers on Instagram. Her endorsement had received more than two million likes on Instagram just half an hour after she posted it.

In her post, Swift urged first-time voters to register and said she would post a link with more voting information on her page.

"I've done my research, and I've made my choice," she said. "Your research is all yours to do, and the choice is yours to make."