Ms Harris has harnessed star power as she focuses on battleground states in her bid for the White House, with Beyoncé, Eminem and Bruce Springsteen among those who have appeared at her campaign events.
In Madison, Wisconsin, American singer Gracie Abrams appeared to address the frustration she said was shared by young voters before Mumford & Sons took the stage.
“We’re Mumford & Sons and there’s nowhere else for us to be,” frontman Marcus Mumford, who is married to British actress Carey Mulligan, told the crowd.
The Brit and Grammy Award-winning band performed hits such as The Cave, Little Lion Man, Awake My Soul and I Will Wait.
“We love this place, we love this state,” Mumford, 37, continued.
“I know it might not sound like it because I grew up in England, but I was born in America.
“I am a native of California and last week it was my great privilege to vote for Vice President Kamala Harris and Governor Tim Waltz for President and Vice President of the United States of America.
“And I would encourage you to get together with your friends, make a plan to vote and get out and vote because every vote will matter to you.”
It came after Abrams performed his songs I Love You, I’m Sorry, Risk and Free Now to a cheering crowd.
“We’ve inherited a world that’s struggling and it’s easy to feel disconnected and disillusioned, between the advent of social media in our childhood and Covid and relentlessly targeted disinformation,” the 25-year-old said.
“We’ve been through some things and it’s easy to get discouraged – but we know better.
“We know that unless we vote and keep our democracy intact, there’s nothing we can do to fix it when it’s our turn.”
Abrams urged the crowd not to give up because “our participation and our voice has never been more important.”
The rally came after “Terminator” star Arnold Schwarzenegger said he would support Ms Harris in the US election on November 5, despite saying “I don’t like either party at the moment”.
The 77-year-old former Republican governor of California, who served from 2003 to 2011, said his party’s nominee, former US President Donald Trump, would “divide”, “offend” and “find new ways to be more un-American than it already was”.
Schwarzenegger said he would vote for Ms Harris and Mr Waltz because he wanted the US to “move forward as a country” despite having “a lot of disagreement with their platform”.
The Austrian-born actor said Mr Trump, who is running for his second term as US president, “will not respect your vote unless it is for him”.
He concluded: “It’s just going to be four more years of nonsense with no results, making us angrier and angrier, more divided and more hateful.
“We need to close the door on this chapter of American history, and I know former President Trump will not do that.
Friends star Jennifer Aniston also confirmed she voted for Ms Harris to “end this era of fear, chaos and attacks on our democracy”.
In an Instagram post, she said: “Today I not only voted for access to health care, for reproductive freedom, for equal rights, for safe schools and for a fair economy, but also for common sense and human decency.
“Please remember that whoever you are and wherever you live, your voice matters. Your voice matters.”