It is part of legislation aimed at bringing "justice, reparation and dignity" to victims of Spain's civil war and the subsequent dictatorship.
Spain's senate has approved a landmark bill that will ban expressions of support for the former dictator Francisco Franco.
The new "Law on Democratic Memory" will also enshrine the memory of Franco's victims and also make the state responsible for searching for missing civil war casualties.
The bill was approved by 128 lawmakers in the Senate on Wednesday, with 113 votes against and 18 abstentions.
The legislation had already been passed by Spain's parliament in July after a lengthy debate.
It is the latest attempt by Spain's Socialist government to heal divisions in the country in the years after Franco's death in 1975.
"We have always been committed to strengthening our democracy and today we are taking another step towards justice, reparation and dignity for all victims," Prime Minister Pedro Sanchez wrote on Twitter after the vote.
In 2019, Spain's government ordered for the former dictator's remains to be exhumed and removed from his monumental mausoleum near Madrid.
Around 114,000 people are still unaccounted for after the 1930s Civil War.
Civic movements have often taken on the responsibility of finding and exhuming victims from unmarked or mass graves, without government funding.
But the "Law on Democratic Memory" forces Spain's state government to search for missing casualties for the first time. A DNA bank will also be created in Spain to help trace, identify, and map out victims of the Franco regime.
The law states that "history cannot be built on the basis of the oblivion and silence of those defeated [in the Civil War]".
Organisations that praise or support the policies and leaders of Spain's 20th-century dictatorship, including the private Francisco Franco Foundation, will now be banned under the legislation.
Any convictions handed down on political, religious, or sexual grounds during the dictatorship will be annulled, and babies who were stolen from Spanish republican families by the Franco regime will also be recognised as "victims".
The bill will also appoint a special prosecutor's office to investigate crimes against humanity during the civil war and dictatorship.
Previous attempts to bring Franco-era officials to justice in Spain have been blocked by a 1977 amnesty law.
NGOs, including the Association for the Recovery of Historical Memory (ARHM), have called for Spain to repeal the 1977 law and further compensate victims of the dictatorship.
But Spain's main right-wing opposition Partido Popular (PP) has repeatedly accused the government of trying to revive the wounds of the past and says they will repeal the new law if elected in 2023.
Spain's former Socialist government passed a law aimed at "historical memory" in 2007 but former PP Prime Minister Mariano Rajoy boasted that he had not used a single euro of public money to support the legislation.