The free add-on, which is due to launch next week, reportedly adds six new character classes, new weapons and a 'Platinum' difficulty level.
The content was discovered by a user on the Something Awful forums, alongside images of the new character classes.
Copyright: EACharacter classes include N7 Fury, N7 Destroyer, N7 Demolisher, N7 Paladin, N7 Shadow and N7 Slayer.
Fury operatives are described as incredibly fast and unpredictable, Destroyers wear the T5-V Battlesuit, making them slow but powerful, while Demolishers can "create a supply pylon that stocks allies with an unending reserve of grenades and thermal reloads".
Paladins, meanwhile, carry powerful omni-shields into battle, Shadows are described as slippery combatants, while Slayers use dizzying sword attacks and are hard to pin down due to their ability to slip fire.
The Mass Effect 3 'Earth' DLC will also add new maps based on London, Rio and Vancouver, according to earlier reports.
Mass Effect 3 'Leviathan' DLC information was recently discovered within the game's 'Extended Cut' add-on.
A partial script outed a new mission revolving around a turncoat Reaper named Leviathan. Sent to rescue a scientist on a mining facility controlled by the traitorous Reaper, Shepard will reportedly be able to recruit the defector and use him as a war asset.
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'
> 'Mass Effect 3' Extended Cut endings revealed - watch
Watch a trailer for Mass Effect 3 below: