The companies said they would cooperate on finding new tools to identify and quickly remove extremist content, such as sharing databases of violent posts or images to ensure they don't spread across multiple platforms.
While it is a voluntary framework, it has been given additional heft after an endorsement from 55 investor funds that will use its $5 trillion in assets to push the tech companies to follow through on their pledges.
Twitter Chief Executive Officer Jack Dorsey, Facebook Vice President for Global Affairs and Communications Nick Clegg and Google Chief Legal Officer Kent Walker will attend the meeting, according to the French president's office.
The White House said on Wednesday it supported the Christchurch Call's aims but was "not in a position to join", citing the need for freedom of speech.
Spokespeople for Macron and Ardern did not respond to requests for comment. The Christchurch perpetrator live-streamed footage of the massacre, which was then disseminated countless times throughout social media.
Facebook and Twitter have already signed on. About 300,000 of those videos slipped through and were published on the site before being taken down by the site's content-moderation teams and blacklist algorithms. It doesn't cost anything for the social tech giants to say that they generally care about maybe somehow stopping actual terrorists from promoting mass murder online.
Ardern is playing a central role in Wednesday's meetings in Paris, which she called a significant "starting point" for changes in government and tech industry policy.
"We continue to be proactive in our efforts to counter terrorist content online while also continuing to respect freedom of expression and freedom of the press", the White House said.
Speaking at her side at the Élysée Palace, Macron said the commitments made today "are part of continuing exchanges between the private sector and heads of state or government". Some have called for giants like Facebook to be broken up.
In Ottawa, the House of Commons committee on access to information, privacy and ethics recently issued a summons for Facebook CEO Mark Zuckerberg and COO Sheryl Sandberg to appear as witnesses in relation to a Privacy Commissioner's report that criticized the company for not doing enough to protect the privacy of Canadian users. The decision puts the United States at odds with USA tech companies including Facebook and Google, which are expected to support the effort. Facebook served as an organizing tool for the deadly neo-Nazi rally in Charlottesville in 2017, for example, and lesser-known fringe websites hosted hateful screeds penned by the man accused of opening fire on a Pittsburgh synagogue a year ago.
Facebook said in its post Tuesday that detecting these videos is an area that needs more research.
"It's a global problem that requires a global response", she said.