Mariano Rajoy is expected in Barcelona, the Catalan capital, at 11am (1000 GMT) to show support for his Popular Party's campaign ahead of a vote next month, AFP reported.
His visit comes two weeks after he dismissed Catalan leader Carles Puigdemont, his government and the parliament, suspended the region's autonomy and called for new elections there on Dec 21.
On Saturday hundreds of thousands of Catalans protested the jailing of regional officials for their push for independence from Spain, which has left the country mired in a political crisis.
The demonstrators gathered on an avenue next to the regional parliament building waving Catalan independence flags and chanting 'Freedom!' while some held up banners announcing: 'SOS Democracy'.
Rajoy, who is due to attend a presentation by a party candidate at a station hotel, will not make a public appearance in the city.
The protest followed the release from jail of the region's parliament speaker - one of dozens of lawmakers sacked by Madrid last month - after posting euro;150,000 euros (RM732, 637) bail.
Children in riding helmets climbed castells - the region's traditional human towers - as others held placards bearing caricatures of some jailed lawmakers.
Barcelona municipal police put turnout for the march at some 750,000 people as crowds stretched for more than 15 blocks along the boulevard.
The Catalonia crisis has caused concern in the European Union as the bloc deals with Brexit and uncertainty over the fate of the region's 7.5 million people. More than 2,400 businesses have moved their legal headquarters elsewhere.
On Wednesday a general strike called by a pro-independence union caused travel chaos, blocking 60 roads and train lines including Spain's main highway link to France and the rest of Europe.
Since lawmakers in Catalonia - a wealthy region with its own language and distinct culture - declared independence on Oct 27 following a banned referendum, pro-separatist officials have come under huge pressure from Madrid.
Barcelona's popular mayor earlier slammed the actions of Puigdemont's government.
'They've provoked tensions and carried out a unilateral independence declaration which the majority do not want,' Ada Colau told a meeting of her party members.
'They've tricked the population for their own interests.'
Eight members of the axed Catalan cabinet are currently detained on charges of sedition, rebellion and misuse of public funds.
A further six fired officials including parliament speaker Carme Forcadell were granted bail this week on similar charges by Spain's Supreme Court.
Puigdemont is in self-imposed exile in Belgium awaiting a hearing on possible extradition back to Spain after Madrid issued an EU-wide warrant.
'The situation is sad, the politicians haven't done their jobs,' said Robert Muni, who was protesting with his children, although some protesters shouted their support for Puigdemont, 'our president'.
Puigdemont and four ex-ministers say they are in Brussels because they cannot be guaranteed a fair trial back home.
'Although some of us are far away from you and others are in prison, we have an opportunity to express loudly and clearly that we want freedom and democracy,' Puigdemont told Catalan television.
Saturday's protest was organized by two pro-independence lobby groups, ANC and Omnium, whose two leaders are also detained.
'We don't know what's going to happen but we know what we want: the release of political prisoners,' said demonstrator Maria Angels Quintana.
Puigdemont has said he travelled to Brussels after declaring independence in order to raise international awareness on the treatment of separatists in Spain.
But the European Union, nervous that Catalan independence could stir up separatist tensions in several member states, has repeatedly backed the government of Prime Minister Mariano Rajoy over the crisis.
Some participants at the rally betrayed their frustration at the lack of support from Brussels for their cause, holding banners printed in English asking 'Europe, where are you?'