Madrid sacked local Catalan leaders including Carles Puigdemont and dissolved the regional parliament after it declared independence from Spain in October.
The crisis in Spain came after a majority of voters backed independence in an illegal referendum, which Madrid tried to stop from happening on October 1.
Scenes of police violence marred the referendum as police tried to seize ballot boxes and clashed with pro-separatist protesters on the streets.
Ahead of the election tomorrow, the latest polls suggest neither the pro-independence nor the pro-unity camp will win a majority of the vote.
The likely outcome is a hung parliament and there are likely to be many weeks of wrangling to form a new regional government in Catalonia.
Mr Puigdemont, the ousted Catalan President, is campaigning for election from self-imposed exile in Belgium where he is staying to avoid arrest in Spain.
His party, Junts per Catalunya (Together for Catalonia), has seen a last-minute boost in the polls.
Junts per Catalunya and the other pro-independence parties — the Candidatura de Unidad Popular and ERC — controlled the Catalan parliament from 2015 until it was dissolved.
The separatist parties are on track to get roughly the same share of the vote as anti-independence parties, according to a poll on Friday by Metroscopia for El País.
The anti-independence parties are the Ciudadanos (Citizens), the PP and the Socialist party. The kingmakers could be the left-wing Catalunya en Comú party, which wants self-determination but not independence per se.
In the separatist heartland of rural Catalonia, fireman Josep Sales says he hopes the results will endorse the result of the independence referendum and lead to the creation of a republic.
“If we get a majority, something will have to be done. And if the politicians don’t do it, the people will unite,” he said, speaking from the town fire station where many of the red fire engines bear the slogan ‘Hello Democracy’.
“If we have to bring the country to a standstill, so be it,” said the 45-year-old, who plans to vote for Carles Puigdemont, the sacked Catalan head who is campaigning for election from self-imposed exile in Belgium.
The uncertainty generated by the independence drive has hurt hotel occupancy rates in the region, dented consumer sales and caused more than 3,000 businesses to move their registered headquarters from Catalonia.
It has also bitterly divided Catalan society between those who support independence and those who favour unity with Spain.
“Everyone is eager for the election and to see how it turns out, because nothing is clear at the moment,” said 34-year-old flamenco teacher Maria Gonzalez, who lives in Cerdanyola del Valles, an industrial suburb of Barcelona.
“The feeling on the streets is not comfortable,” says Gonzalez, the daughter of migrants from other parts of Spain who moved to Catalonia decades ago and who plans to vote for pro-unity party Ciudadanos.
“There’s a hidden tension.”