The inquiry head, Justice France Charbonneau, has asked Premier Pauline Marois to push the deadline back another 18 months.
Charbonneau says the additional time is needed for the probe to finish its work and make recommendations in a final report.
She indicated the commission's final report would be available in about two years, no later than April 19, 2015.
The government said in a statement that the request has been sent to cabinet for study and no decision has been made. However, Premier Pauline Marois has already offered a strong hint that she would be inclined to accept an extension request.
The commission was ordered in 2011 by then-premier Jean Charest after intense pressure, and was mandated to produce a report by this fall.
So far, the probe has heard incendiary testimony about rampant corruption in public procurement — with the Italian Mafia, political parties and crooked bureaucrats supposedly involved in a number of schemes.
But the inquiry has focused almost exclusively on municipal politics so far, and has barely dipped its toe beyond Montreal. It prompted the resignation last fall of the mayor of Montreal, Gerald Tremblay, following claims from a witness whose testimony is now under attack.
Observers have speculated for months that the inquiry appeared to be running out of time and would inevitably need to request a deadline extension
A change in the schedule could hold a number of political implications.
The Parti Quebecois has a minority government. The schedule delay could mean that the politically explosive probe is still ticking in the province's political arena while the government approaches the fourth year of its mandate.
It could extend the life of corruption issues as a defining force in Quebec politics.