Mr Puigdemont and his deputy Oriol Junqueras will “proclaim the Catalan Republic on Monday”, according to local media reports.
Catalans voted overwhelmingly for autonomy from Spain in a historic but highly controversial referendum on October 1.
Spain’s central government in Madrid has ignored the result of the poll and has threatened to impose direct rule on Catalonia.
Despite warnings he could be arrested, the president is believed to be pushing ahead with a unilateral declaration of independence.
A source told Spanish news website El Confidential: “Puigdemont knows he can end up in jail, but that does not matter to him.
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“He is more interested in presenting himself as a martyr. Economically, Catalonia has little to lose.
“Not even personally, since his wife and children are no longer in Spain. And politically it can favor him.”
Mr Puigdemont last night branded Madrid’s move as the worst attack on Catalonia’s institutions since the Franco dictatorship.
He also accused the Spanish government of “slamming the door” on his pleas for dialogue to resolve the political crisis.
Hours later, the Catalan government vowed to fight “tooth and nail to defend Catalonia’s democratically elected institutions”.
Government spokesman Jordi Turull said the coming week would be one “where decisions are taken, adding: “Doing nothing doesn’t figure in our plans.”
Prime Minister Mariano Rajoy is asking for authorisation to sack the regional government including Mr Puigdemont and Mr Junqueras.
Central government will take over the regional administration until calling fresh elections within six months of direct rule coming into force.
On Saturday, Mr Rajoy said he wanted to convene a vote “as soon as we get back to institutional normality”.
The Economy Ministry has already increased its control over regional finances, to block the use of state funds to organise the secession bid.
The Senate, where Mr Rajoy’s People’s Party has a majority, will vote on the proposal on October 27.
The opposition Socialist and Ciudadanos parties are backing Mr Rajoy.
After the measures are approved, they can be activated immediately or put on hold to be implemented in the future.
Mr Puigdemont could call an election himself before Madrid’s plan comes into action, in which case direct rule would likely not be implemented.