The revised ending will be available as a free download on Xbox 360, PC and North American PlayStation 3 on June 26. The DLC's launch on PlayStation 3 in Europe is pushed back to July 4, though it will still arrive on other platforms on the June date.
Bioware says that the new content will not replace the existing ending, but expand on it with additional scenes and an extended epilogue.
"It gives a sense of what the future holds as a result of the decisions made throughout the series," Bioware said. "And it shows greater detail in the successes or failures based on how players achieved their endings."
After Mass Effect 3 released, users were disappointed by the game's ending and began social media campaigns to convince Bioware to change it.
Some users even filed complaints against publisher Electronic Arts for false advertising. While the UK's Advertising Standards Authority ruled the game was not misleading, the Better Business Bureau in the US ruled in favour of the fans.
Mass Effect 3 shipped 3.5 million copies worldwide during its first week on sale, making it the biggest entertainment launch of the year, according to publisher Electronic Arts.
Mass Effect 3 is available on Xbox 360, PS3 and PC. A Wii U version was also confirmed during E3, which will include all existing DLC.
> Read Digital Spy's review of 'Mass Effect 3'
Watch the Mass Effect 3 Extended Cut interview trailer below: