The Vita exclusive reportedly takes place in New Orleans after the end of the 18th-century French and Indian War.
It stars a female assassin named Aveline, reports Game Informer (via NeoGAF).
The title will feature "true Assassin's Creed gameplay", but does not connect to Desmond, although it is said to feature a meeting between Aveline and Connor.
Liberation is said to include multiplayer, which has been "specifically tailored for the Vita experience".
Players will be able to use front and rear touch controls to pick pockets.
It will be developed by Ubisoft Sofia and released on the same day as Assassin's Creed 3.
> E3 2012: Digital Spy's coverage from the world's biggest gaming expo
> Assassin's Creed 3 first-look preview
More details will be announced at Ubisoft's E3 press conference later tonight (June 4).
Announced in March, Assassin's Creed 3 will take place over a 30-year period in colonial America beginning in 1777.
It features a brand new lead named Connor, the offspring of an English father and Native American mother.
New abilities are expected to feature in the game, such as climbing trees and hunting wildlife. Ubisoft president Yves Guillemot has called Assassin's Creed 3 the "biggest in the series to date".
Releasing on October 31 worldwide, Xbox 360, PC, PlayStation 3 and Wii U editions have so far been confirmed.
The E3 Expo will take place in Los Angeles from June 4 to June 7.
View a trailer from Assassin's Creed 3 below: