The decision was closely followed in Spain, where the governing Socialists are seeking to convince Esquerra Republicana, the Catalan party of jailed separatist leader Oriol Junqueras, to support plans for Sanchez to form a new government.
The Socialists are the biggest party in the Spanish Congress, with 120 seats, and have announced a coalition agreement with Unidas Podemos, which holds 35 seats.
Still, the partners need more support to ensure a majority in the 350-member chamber, including that of Esquerra Republicana.
With Junqueras potentially leaving prison, the chemistry of the negotiations to form a government may change as the balance of political power in Catalonia also changes.
Legal immunity
“The ECJ has said Oriol Junqueras was right and recognises that he had immunity,” ERC said on Twitter. “We demand the judgment be annulled and immediate freedom.”
The decision also has implications for Carles Puigdemont, the former Catalan president who led the illegal bid to break away from Spain in 2017.
Puigdemont, who is in exile in Belgium and faces arrest if he returns to Spain, was also elected as an MEP.
The decision will strengthen the position of Puigdemont, who may feel emboldened to press for regional elections in Catalonia, putting pressure on ERC, according to LLuis Orriols, a political scientist at Carlos III University in Madrid.
“The negotiating position for Esquerra is weakened but talks with the Socialists also seem well-advanced.”
“It’s a clear victory for the independence movement and potentially a political earthquake,” said Orriols.
Coalition support
Esquerra officials have repeatably claimed that it’s difficult for them to consider supporting a Sanchez government while Junqueras is serving a 13-year prison sentence for his role in the botched 2017 illegal independence proclamation in Catalonia.
Junqueras was elected to the European Parliament in May.
His lawyers claimed he has legal immunity because of his election as an MEP. If Junqueras were to be freed, that would enable him to personally take part in the negotiations with the Socialist party.
“A person elected to the European Parliament acquires the status of member of that institution at the time of the official declaration of the results and enjoys, from that time, the immunities attached to that status,” the court said in a ruling handed down in Luxembourg.
Esquerra, a left-leaning party, was crucial in the no-confidence vote that removed Mariano Rajoy of the conservative People’s Party as prime minister and installed Sanchez in 2018.
However, earlier this year, Sanchez called snap elections when ERC voted against his budget proposal.
The elections were held in April but after failing to form a government, Sanchez called a second ballot which was held last month. Another inconclusive result in that vote caused him to reach out to Junqueras’s ERC for support.