"We Catalans demonstrated to the world that we have the capacity and the will to become an independent state. And on (December) 21, we must ratify this," he said in Oostkamp in Belgium, where he travelled after the Catalan parliament declared unilateral independence.
Puigdemont was sacked as Catalan president after that declaration on October 27 as was his entire regional government. Madrid imposed direct rule on the once semi-autonomous region to stop the independence drive.
At the time, Spanish Prime Minister Mariano Rajoy also dissolved the Catalan parliament and called next month's elections in a bid to "restore normality" to the region.
Puigdemont, who is awaiting possible extradition to Spain where he is wanted on charges of rebellion, sedition and misuse of public funds, is running at the head of the Junts per Catalunya ("All for Catalonia" in Catalan) grouping.
It comprises people from his conservative, separatist PDeCAT party as well as members of civil society.
Puigdemont had hoped to form a united separatist front for the new elections, as was the case in the region's last elections in 2015, when the pro-independence camp secured a majority of 72 seats in the 135-seat parliament, even though it won just 47.8 percent of the vote.
But ERC -- the party of his former vice-president Oriol Junqueras, who stayed in Spain and was remanded in custody by a judge investigating him and other former regional ministers on the same charges as Puigdemont -- rejected a joint ticket.
Opinion polls suggest that ERC is leading in the current campaign, which officially opens on December 5.
"This moment transcends political parties," Puigdemont said in Oostkamp.
"It's time for us to be activists for Catalonia, which is what people want."
It is unclear whether Puigdemont will still be in Belgium when the elections take place.
If Belgium decides to extradite him to Spain, he faces jail pending a probe into the charges against him.
Spanish MEP Esteban Gonzalez Pons, a member of Rajoy's conservative Popular Party, said Saturday it was "surreal" that Puigdemont was launching his campaign from Belgium.
"He's not in exile in Brussels, but looking for a hideout. Puigdemont doesn't live in Brussels, he's hiding there," he said in an event in Ibiza.
The separatist crisis began in earnest on October 1 when separatist leaders held an independence referendum despite a court ban, in which they said 90 percent opted to break from Spain even if less than half of eligible voters turned out in the deeply divided region.
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