The election on Thursday is being held in exceptional circumstances as it was ordered by the Spanish government when it seized control of the region, dismissed its government and dissolved the regional parliament following a declaration of independence by separatist lawmakers there on 27 October.
Several members of the ousted cabinet, including former Catalan president Carles Puigdemont, are campaigning from Brussels where they have taken refuge from Spanish justice, while others are in jail in Spain on provisional rebellion charges.
Mr Puigdemont is to close his re-election campaign with a video speech to be relayed at a rally for his Together for Catalonia party in Barcelona.
His former deputy president, Oriol Junqueras, of the ERC leftist republican party, is in jail outside Madrid where his campaigning is curtailed.
The parties of Mr Puigdemont and Mr Junqueras, along with a small anti-capitalist group, held a slim majority in the last parliament, enabling them to push ahead with the independence drive, but it remains to be seen whether they can stick together after Thursday’s election.
Recent polls indicate the vote will be a close race between Mr Junqueras, Mr Puigdemont and Ines Arrimadas of the pro-Spanish unity Ciutadans (Citizens) party, but no group is likely to win a majority.
Spain has said it will return full autonomous powers to Catalonia once a law-abiding government is elected.
Polls consistently show most Catalans want the right to decide their future but are evenly divided over splitting from Spain.