Released earlier today, the free DLC adds new endings elaborated on the three choices available to players at the end of the game.
It also added a fourth new ending, which is unlocked by refusing to co-operate and accept any of the choices given to you.
The 1.85GB download is available to download now on Xbox 360 and PC, and will be released on PS3 from July 4.
> Download the Mass Effect 3: Extended Cut DLC from the Xbox Live Marketplace
Mass Effect 3: Extended Cut is the result of a fan campaign against BioWare and Electronic Arts.
Some users filed complaints against publisher Electronic Arts for false advertising, claiming that the game's endings were too similar.
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.
Yesterday, BioWare admitted that the extended ending would add value and closure, but would not satisfy everybody.
> Read Digital Spy's review of 'Mass Effect 3'
Screenshot gallery - view Mass Effect 3 screens below: