Former health minister Philippe Couillard, former finance minister Raymond Bachand and former transport minister Pierre Moreau have met the deadline for submitting their candidacy papers for the party leadership.
They will participate in a series of four French and one English debates before the leadership convention on March 16-17.
Couillard, a former doctor who is considered to be the frontrunner, quit politics in 2008 but says he wants to turn the Liberals into a party of ideas.
Charest quit after the Liberals lost the Sept. 4 election to the Parti Quebecois.
Although allegations of corruption swirled around his government before the election, Pauline Marois took power with only a bare minority and has had a rough start to her administration.
The Liberals are now being led on an interim basis by Jean-Marc Fournier.