Carles Puigdemont, the former leader of Catalonia who fled Spain over his role in a failed 2017 independence bid for the wealthy region, returned to Spain on Thursday after seven years on the run despite a pending arrest warrant.
Puigdemont shouted "Long live a free Catalonia!" as he climbed onto a stage in Barcelona to address thousands gathered near the Catalan regional parliament which is set to elect a new leader later in the day.
"I have come here to remind you that we are still here," he added to applause.
Many in the crowd waved red, yellow and blue Catalan independence flags and chanted slogans demanding Catalonia's secession from Spain.
"He is a very noble person, the only one who believes in independence and has not stopped believing," said Nuria Pujol, a woman in her fifties who came to Barcelona from the Alt Penedes region in the interior of Catalonia to see Puigdemont.
After his brief address, Puigdemont headed to the regional parliament for the investiture vote where it is expected that police will detain him before he can enter.
If that happens the vote will likely be suspended.
After months of negotiations following an inconclusive May regional election, the leader of the local branch of Spain's ruling Socialists -- Salvador Illa, who is close to Prime Minister Pedro Sanchez -- is poised to become Catalonia's new leader.
The Socialists won the most seats in the northeastern region but failed to get a majority.
Illa then secured the support of a tiny far-left party and leftist Catalan separatist party ERC, giving him the needed 68 votes to be elected in Catalonia's 135-seat parliament as leader of the regional government.
The investiture debate is set to begin in the Catalan parliament at 10:00 am (0800 GMT).
The secretary general of Puigdemont's hardline separatist party JxCAT has said he would call for the vote to be suspended if the former Catalan leader is arrested.
If a new Catalan regional government is not formed by August 26, fresh elections will be held in October.
Puigdemont led the regional government of Catalonia in 2017 when it pushed ahead with an independence referendum despite a court ban, which was followed by a short-lived declaration of independence.
He fled Spain shortly after the independence bid to avoid prosecution and has since lived in Belgium and more recently France.
While Spain's parliament in May passed an amnesty law for those involved in the botched secession bid, the Supreme Court ruled on July 1 that the measure would not fully apply to Puigdemont.
Sanchez agreed to the amnesty law in exchange for JxCAT's crucial support in Spain's parliament for his fragile minority government, sparking huge street protests against the measure organised by the right.
He is now facing opposition from parts of his own Socialist party as well as the right over a proposal to give Catalonia full control of the taxes collected in the region.
The measure was promised the ERC in exchange for the party's support for Illa in Thursday's investiture vote.
The proposal has for decades been one of the main demands of Catalan independence parties but critics argue it would deprive the central state of a substantial source of revenue. It still must be approved by Spain's national parliament.
A similar system already exists in Spain's northern Basque Country, which also has an active independence movement.
If Illa passes Thursday's investiture vote, he will be the first head of Catalonia's regional government who does not come from the separatist camp since 2010.
The former health minister has defended the tax agreement made with the ERC, saying they are "in favour of all Catalans".
"They are agreements to improve our financing without harming anyone and maintaining criteria of solidarity," he said after securing the ERC's support.
But former Socialist deputy prime minister Alfonso Guerra has warned the tax agreement opens "a path towards a federal system and the independence of Catalonia".
