The surprise news broke as a who's who of the Quebec sovereignty movement gathered in Montreal for the state funeral of former Quebec Premier Jacques Parizeau.
Until Tuesday, Duceppe was thought to be only assisting and advising current leader Mario Beaulieu on the upcoming campaign. The veteran leader was a strong debater in past campaigns.
It's unclear in what riding Duceppe would run or what process would see him take the party's reins from Beaulieu, who does not currently have a seat in the House of Commons.
Duceppe had both criticized and expressed support for Beaulieu's leadership on various occasions.
Veteran BQ MP Louis Plamondon told reporters covering question period on Monday that Duceppe's presence and participation in the approaching campaign would be a "big plus" for the sovereignty movement.
In French, he also said Duceppe has "extraordinary credibility with all Quebecers."
Plamondon downplayed the BQ's crushing defeat in Quebec in the 2011 election, when it was reduced from 47 seats at dissolution to only four, losing official party status in the process.
Plamondon said Monday that the loss was not a rejection of the BQ, but an expression of sympathy for Jack Layton's NDP. He called it a "blip" and said the Bloc is still needed in Ottawa.
Comeback possible after infighting?
The party will have nominated 40 candidates by the end of June, he said, and he expressed optimism about a comeback.
But defections and departures over policy differences have left the BQ with only two seats, and only Plamondon intends to run for re-election.
Beaulieu's hardline approach to sovereignty has alienated soft nationalist support for the party and has cost it both MPs and members.
The party's vice-president, Annie Lessard, left late last year over personality differences with Beaulieu.
Last October, former BQ leadership challenger Jean-François Fortin joined forces with a New Democrat to create a new party, Forces et Démocratie, that is fielding candidates in Quebec this fall. The new party focuses less on sovereignty and more on better representation for Quebec's regions in Ottawa.
Fortin called Beaulieu's leadership approach divisive and radical.
Duceppe was rumoured to be interested in a jump to provincial politics and had been courted to lead the Parti Québébois. But he never followed through and actually ran for the leadership.
In 2012, he insisted he was finished with politics, federal or provincial.