Deputy Prime Minister and Liberal Democrat Leader Nick Clegg will lead the debate in Parliament in favour of the referendum.
MPs will be debating the Parliamentary Voting System and Constituencies Bill on their first day back from the summer recess.
Commenting, Liberal Democrat deputy leader, Simon Hughes said:
"We have a unique opportunity to overthrow our archaic voting system and replace it with something fairer and better.
"Liberal Democrat activists, alongside those from other parties and none, have long campaigned for a new voting system.
"The Alternative Vote is a system that accommodates more choice while making sure no MP is elected without 50% support from their consituents.
"It will also make MPs work harder to win and keep support. Good MPs will have nothing to fear from AV - only bad MPs will want to keep the current system."
To sign up for the Liberal Democrat campaign for fairer votes, visit www.libdemsforfairervotes.org.uk."