The video endorsement, via Instagram, was made on National Voter Registration Day to stress the importance of voting.

Eilish and Finneas urged followers to vote for Harris-Walz to protect reproductive freedom, the planet and democracy.

They encouraged early voting and registering on iwillvote.com.

The development follows a similar move by fellow popstar Taylor Swift who endorsed Harris last week. 

Elon Musk reacted to Swift's endorsement with a tweet offering to "give you a child and guard your cats with my life"

Musk's tweet went viral, amassing 96  million views and 400 000 likes by Thursday.

Musk's comment drew online backlash, with many labeling it as inappropriate and bizarre.

In response to his tweet, one X user wrote: "Cats politely but firmly decline your offer. Now stop being weird and offering your children to people."

Another quipped: "Will Taylor Swift fans ever buy a Tesla now?"

On Instagram, Swift praised Harris as a "steady-handed, gifted" leader fighting for crucial abortion, in vitro fertilization and LGBTQ+ rights.

Swift also criticized Trump's fake AI images showing her endorsing him.

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

Swift's endorsement follows her support for Biden-Harris in 2020.

A CNN poll found that the majority of respondent believed Harris outperformed Trump in the debate.

Swift urged first-time voters to register and vote early, and signed off her post with "Taylor Swift, Childless Cat Lady," taking a jab at comments made by Trump's running mate, J.D. Vance.