Spain's parliament gave the final green light to a controversial amnesty bill for Catalan separatists on Thursday, paving the way for the return of their figurehead Carles Puigdemont after years of self-imposed exile.

The legislation seeks to draw a line under years of efforts to prosecute those involved in the botched 2017 Catalan independence bid that triggered Spain's worst political crisis in decades.

The text, which has been resolutely opposed by Spain's right and far-right opposition, passed by 177 votes in favour to 172 votes against in the 350-seat parliament. One person was absent from the vote.

Passing the amnesty is a key moment for Socialist Prime Minister Pedro Sanchez, as it was a demand made by separatist parties in exchange for their parliamentary support to allow him to serve a new term.

In March, Spain's lower house of parliament passed the bill, which grants an amnesty to hundreds of separatists involved in Catalonia's failed 2017 independence bid.

It then went to the Senate upper house, which is dominated by the right-wing opposition, where it was symbolically vetoed – as the Senate cannot block a bill, but only propose amendments – before returning to the lower house on Thursday morning.

Following a rowdy two-and-a-half hour debate during which the Speaker was forced to call order several times due to the insults traded on the floor, the bill passed.

It will now be up to individual judges to decide whether the amnesty applies to their cases. They have two months to raise issues with the Constitutional Court or the European justice system which could delay the law's implementation for some time.

The biggest beneficiary will be Puigdemont – the former Catalan leader who led the bid then fled Spain to avoid prosecution.

His hardline separatist JxCat and its moderate rival ERC both demanded the amnesty in return for their votes in November that let Sanchez secure another four-year term.

What opened that door was Spain's inconclusive July 2023 election, which was won by the right-wing Popular Party (PP) but without enough parliamentary support to form a government.

With JxCat cast as kingmaker, Sanchez won them over with the promise of an amnesty and returned to office, in a move sparking fierce and unrelenting opposition from the PP and the far-right Vox.

They have drawn thousands onto the streets in mass protests against the bill that at times turned violent, notably around the Socialists' Madrid headquarters.

Earlier this week, a PP spokesman said that even after it passes, the party would do everything to "overturn" the law, whether through appeals to the Constitutional Court or "social pressure" on the street.

Surveys suggest Spaniards are divided over the amnesty, even Sanchez's own Socialists and their supporters.

However, the outcome of Catalonia's regional election on May 12, in which the Socialists won a clear victory, has shifted the picture.

The separatists lost their absolute majority in the Catalan parliament after 10 years in power, suggesting the focus has shifted away from independence, vindicating Sanchez's strategy of seeking to defuse tensions around the 2017 crisis.

The leader of the Socialist Party's Catalan branch, Salvador Illa, is hoping to lead the region's new government.

The results show that Catalonia has chosen "the path of forgiveness, giving up any kind of resentment," Sanchez said in Barcelona last week.

Puigdemont, whose party increased support during the vote and has said he wants to lead a minority separatist administration, is hoping to be home back in time to see a new Catalan government take office.

Although the date has not yet been set, it is expected to take place by June 25 at the latest.

But it is unclear whether that will be possible, given the two month time span for the courts to enact the legislation, which involves releasing those behind bars and cancelling outstanding arrest warrants, including the one for Puigdemont. (AFP)