Mr. Puigdemont and the separatists are waging a high-stakes battle with the Spanish government over independence, touched off by an Oct. 1 referendum that the Spanish government says should never have taken place because it violated Spain’s Constitution.
Prime Minister Mariano Rajoy of Spain called the elections for later this month in the hope that voters would replace the separatists who had used their fragile majority to push through the independence referendum that Spanish courts had declared illegal. Mr. Puigdemont is hoping to run for re-election from Brussels.
The judge’s decision on Tuesday followed mounting concerns among Spanish legal experts that the Belgian judiciary could, in effect, limit the range of crimes for which Mr. Puigdemont and the others could be charged if they returned to Madrid.
That could also mean that Mr. Puigdemont would end up being prosecuted in Spain for less serious crimes than those faced by his former deputy and by other former members of the Catalan government who pushed for the region’s unilateral independence from Spain, but who agreed last month to be summoned before a Spanish judge.
In his ruling on Tuesday, Judge Pablo Llarena of the Supreme Court said that it was important to keep “unity” in the legal proceedings against the separatist leaders and to avoid having those who stayed in Spain being at a disadvantage compared with “the fugitives.”
He made his decision a day after ordering that four separatist leaders, including Oriol Junqueras, the ousted deputy leader of Catalonia, be kept in jail. Six other former members of the Catalan government were released, however, after posting bail of 100,000 euros, or about $120,000, each and pending a full trial.
Mr. Puigdemont said that he and the former cabinet members had traveled to Belgium because they felt they would not receive a fair trial in Spain, but they were not seeking asylum.
“We are here because Brussels is the capital of Europe — it is not a question of Belgian politics,” Mr. Puigdemont said after arriving. “This is a European issue, and I want Europe to react.”
A lawyer for Mr. Puigdemont said last weekend that Mr. Puigdemont and the four former Catalan ministers intended to stay in Belgium until after the Catalan elections, and possibly beyond that. Since his arrival in Belgium one month ago, Mr. Puigdemont has staged a few campaign events there, at one point inviting more than 500 Catalan mayors. He is expected to rally 20,000 Catalans in Brussels on Thursday, according to officials.
European leaders, however, have been largely unsympathetic to the Catalan push for independence, and Belgian leaders did not exactly welcome the separatists with open arms.
The presence of Mr. Puigdemont created a political problem for Prime Minister Charles Michel of Belgium, who wants to maintain good relations with Spain but must also be mindful of the Flemish separatist party that is part of his governing coalition. The idea of asylum for the Catalan separatists “is absolutely not on the agenda,” Mr. Michel said last month.
The international arrest warrant for Mr. Puigdemont and the other separatists was issued on Nov. 3. They turned themselves in to the Belgian police two days later, and were taken into custody on Nov. 6 but then quickly released, albeit with strict conditions.