On the last day of the fiercely-fought campaigns for Sunday's vote, Mariano Rajoy appeared in a video appealing to voters in the rich northeastern region to stay with Spain.
Catalan leaders' determination to cast Sunday's election as a vote on independence has placed them in a bitter standoff with the Spanish government, which says secession would be illegal.
"United we will win," said the bearded premier in Catalan, to the tune of sad piano music, in Friday's video following similar entreaties by senior members of his conservative Popular Party (PP) - a brief conciliatory gesture at the climax of a combative campaign.
Various groups including the PP and the "Together For Yes" independence alliance had scheduled major rallies in Catalonia on Friday evening to close their campaigns.
Catalonia's regional president Artur Mas told AFP in an interview this week that he will consider a victory on Sunday for his nationalist alliance tantamount to a "Yes" vote for independence.
If his side wins, he vows to launch a roadmap towards a declaration of independence by 2017.
The Catalan issue poses a tough challenge to Rajoy as he seeks to cement Spain's recovery from recession.
US President Barack Obama and British premier David Cameron, among other foreign leaders, have called for Spain to stay united.
Spanish officials have threatened Catalans will be stripped of their nationality and warned they will plunge into financial chaos like Greece if they break away.
Mas accused his opponents of waging a "campaign of intimidation".
He said that if he wins the vote, Catalonia will leave Spain to pay off the region's debt if Madrid doesn't sit down to talk.
The latest opinion polls show Mas and his allies could win a majority in the Catalan parliament and nearly half the votes overall.
What would happen then is uncertain.
Depending on who wins the Spanish general election in December, Mas could soon have a new leader to talk to in Madrid.