Eilish, 22, said: “We are voting for Kamala Harris and Tim Walz because they are fighting to protect our reproductive freedom, our planet and our democracy.”
O’Connell, 27, added: “We can’t let extremists control our lives, our freedoms and our future. The only way to stop them and the dangerous Project 2025 agenda is to vote and elect Kamala Harris.”
Eilish continued: “Vote like your life depends on it, because it does.”
The post is likely to spark the wrath of Trump, who declared he “hates” Taylor Swift a few days after she also endorsed his political rival.
He raged online in an all-capitalised message: “I HATE TAYLOR SWIFT!”
The Cruel Summer hitmaker had pledged her support in an Instagram message which drove more than 400,000 visitors to the vote.gov site in under a day.
She said: “I will be casting my vote for Kamala Harris and (her vice president nominee) Tim Walz in the 2024 Presidential Election.
“If you haven’t already, now is a great time to do your research on the issues at hand and the stances these candidates take on the topics that matter to you the most … as a voter, I make sure to watch and read everything I can about their proposed policies and plans for this country.”
Swift also used her note to blast images generated by artificial intelligence that were reportedly shared by the former president on Truth Social that suggested she was backing him to return to the White House.
She said: “Recently I was made aware that AI of ‘me’ falsely endorsing Donald Trump’s presidential run was posted to his site.
“It really conjured up my fears around AI and the dangers of spreading misinformation.
“It brought me to the conclusion that I need to be very transparent about my actual plans for this election as a voter.
“The simplest way to combat misinformation is with the truth. I’ve done my research, and I’ve made my choice. Your research is all yours to do, and the choice is yours to make.”
In a dig at Trump’s running mate JD Vance, 40, and his infamous jibe at women who didn’t have children, the singer signed off her post as: “Taylor Swift, Childless Cat Lady.”