The legislation was backed by Spain's left-wing coalition government, two Catalan separatist parties, and other smaller parties.
It passed on Thursday by a vote of 177-172 in the lower house, with the conservative Popular Party and far-right Vox opposing it.
The amnesty could benefit former Catalan regional president Carles Puigdemont, who is a fugitive from Spanish law in Belgium after fleeing his country following the failed October 2017 breakaway bid that he led.
It should also help out hundreds more, including former government officials in Barcelona, average citizens who took part in the secession attempt or protests, and some police officers involved in the crackdown on an illegal independence referendum held by Puigdemont's government.
The amnesty could benefit former Catalan leader Carles Puigdemont, who is a fugitive in Belgium. (AP PHOTO)
The passing of the amnesty law, however, does not immediately clear up the legal mess of the separatists.
The law is likely to face legal challenges and will be reviewed by higher courts. It also must be applied by courts on a case-by-case basis.
There are experts who question its constitutionality since they say it would create inequality between Spanish citizens by favouring some over others.
Since taking power in 2018, Spanish Prime Minister Pedro Sanchez has focused on reducing tensions in northeast Catalonia and he argues that the amnesty is key to culminating that process.
But the amnesty was also a political necessity for Sanchez, who agreed to the act of pardon when he needed the support of the separatist MPs in Madrid to form a new national government in November.
It was initially approved by the lower house in March.
The Senate, where right-wing parties hold a majority, vetoed it earlier this month, but the lower house pushed it through regardless.
While the amnesty is popular in Catalonia, even among many unionists, the Popular Party and Vox have led protests against it in Madrid and other cities across the country.
There have also been critics of the amnesty within Sanchez's Socialist party.
It comes during the run-up to European Parliament elections on June 6-9 and when the Socialists are trying to form a government in Catalonia after beating the separatists in regional elections earlier in May.
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