The US "had" to join the Christchurch Call after social media played a vital role in organising the January 6 insurrection, says a leading expert.
The Christchurch Call to Action was initiated by New Zealand Prime Minister Jacinda Ardern in Paris almost two years ago following the March 15 terror attacks in Christchurch.
It aims to eliminate all terroristic and extremist content from online platforms.
Former President Donald Trump refused to join, but Biden accepted the call on Saturday.
Eric Feinberg, vice president of Coalition for a Safer Web, told The AM Show the Capitol riot proved the US could no longer stand back.
"I think it shows how the [Joe] Biden administration is acting more as the US should be - as a world leader, especially on this issue," he said on Monday.
Ardern says she is glad the US is on board.
"It's something that we have been working on from the very beginning [having the US involved]....social media platforms are not a place for violent extremists and terrorists. Right from the beginning the United States has been involved, they have been working closely with us, they just haven't signed on."
She would not say whether it was Trump's influence which caused the hold up from the US.
"It's not for me to explain the decision making of the United States," she told The AM Show.
"It's fair to say that certainly this [Biden] administration has said this is a priority for them and they have said that they will participate."
Big tech firms including Amazon, Facebook, Google and Twitter all signed up to the pledge, with Ardern saying last month that it was unrealistic to expect the internet to be free from all content that is of concern and the goal was to get "meaningful progress" to reducing the content.
Feinberg says the USA's participation will add weight to the movement.
"Most of these tech companies are in the US - what weight did it have when the US was on the sidelines, when all these platforms are located in the US?"
He says tech companies must be held accountable for the content hosted on their site - especially in the wake of the insurrection.
"Look back on how these platforms were used for the Capitol attack...when I look on January 6 and that attack on our Capitol and for [social media companies] to treat it like nothing happened - you have to be angry, and no one wants to see it again."
More than 200 people have been arrested for their parts in the riot which killed five people - and hundreds of posts on social media have shown the attack was planned and coordinated not just though encrypted apps but on blogs, forums and messenger services.
"Terrorism on social media is a real problem," says Feinberg.
"Think of the former presidency - the Capitol insurrection was organised through social media encrypted apps so we have to be engaged to avoid that happening again."
It's not just a US problem - Feinberg says videos of the Christchurch terror attack are still available online - despite promises from social media companies they will be removed.
Just days after the 2019 atrocity, the Chief Censor declared the video - shot in a first-person view, like a videogame - objectionable. The same went for the killer's manifesto, which was uploaded to free-for-all website 8chan. Anyone found to be distributing either could face up to 14 years in prison or a $10,000 fine.
Feinberg says it's unacceptable the content is still being shared.
"We gotta stop taking the word of the social media companies that say they're removing this and then not doing it."