However, Endgame was sitting just $500,000 (£399,902) behind on Friday at $2,789.2 (£2,230.82) billion, meaning the record will be broken by the end of the weekend (if not already).
On Saturday, Disney and Marvel's blockbuster crossed $US2.7892 billion ($A3.9608 billion) at the global box office.
Nearly as if it were orchestrated months ago, Marvel Studios president Kevin Feige on Saturday took to the stage at the hallowed Hall H of the San Diego Comic-Con, where the idea of the MCU was first revealed to the world in 2007, to announce that Avengers: Endgame had become the highest grossing film of all time.More news: 'Game of Thrones' cast defend final season at Comic-Con
In a statement, Alan Horn, Disney Studios co-chairman and chief creative officer, said the record was a testament to the "power of movies".
Projections place Endgame ahead of Avatar in box office rankings, with a lead of about $2 million at the time of this writing.
After their appearance, it was announced at the fan event that Marvel's Avengers: Endgame had now become the highest grossing movie of all time.More news: Emery confident Arsenal will soon have 'three or four' new players
Fans watch Avengers figures before an early premiere of "The Avengers: Endgame" movie in La Paz, Bolivia, April 24, 2019. "The talented filmmakers behind these worlds have much more in store, and we look forward to the future of both the Marvel Cinematic Universe and Pandora".
"Avengers: Endgame" features Robert Downey Jr.as Iron Man, Chris Evans as Captain America, Brie Larson as Captain Marvel, Chris Hemsworth as Thor, Scarlett Johansson as Black Widow, Mark Ruffalo as Hulk and Paul Rudd as Ant-Man. It's the #1 release of all time in 25 territories, and the #3 highest grossing film of all time in China with $629M.
Since Disney closed its $US71.3 billion acquisition of Fox, Avatar is now part of the Disney empire. Which is perhaps not all that surprising, given that Disney also now controls Fox, home of Cameron and Avatar.More news: Mariners' Mike Leake tosses one-hitter in rout of Angels
Cameron is scheduled to release four Avatar sequels starting in December 2021.