He won the most votes in the last ballot in April but failed to gain enough parliamentary support to form a government.
All predictions suggested that the Right-of-centre bloc comprising the PP, Vox and liberal Ciudadanos would fall short of a majority - as would the sum of the Socialist party, Podemos and other Left-wing forces.
Failure to reach agreement between the Socialists and United We Can, Spain's fourth largest party in parliament, following the last election in April was one of the main reasons for the calling of Sunday's vote, the fourth in as many years.
One of the major focuses of Sunday's election is the northeastern region of Catalonia.
Spain's supreme court sentenced former separatist Catalan leaders to prison for illegally holding an independence referendum two years go. Many injuries were reported when they clashed with police. REUTERS/Sergio Perez Spanish acting Prime Minister and Socialist Workers' Party (PSOE) leader Pedro Sanchez takes a selfie with a supporter during a campaign closing rally ahead of general election, in Barcelona, Spain November 8, 2019.
The conservative Popular Party follows in second place, while the far-right Vox party appears to have doubled its vote share, said the poll by public broadcaster RTVE.
Spain, a country which returned to democracy after a near four-decade right wing dictatorship under late Gen. Francisco Franco, used to take pride in claiming no far-right group had seats in the national parliament, unlike the rest of Europe.
Meanwhile, polls show Vox is on track to nearly double its seats in Parliament, leapfrogging Podemos and Ciudadanos to become Spain's third largest party after taking a hardline stance against separatism. No party is expected to win a majority on Sunday.
Voting will begin at 9:00 a.m. local time. The result will be known by midnight.