Two pro-independence Catalan politicians received accreditation to sit as members of the European Parliament after a court ruled that Spain had no right to block them.
Former Catalan regional president Carles Puigdemont and his health minister Toni Comin arrived at the parliament in Brussels to collect their badges in front of a crowd of reporters.
Wearing his blue parliamentary pass Mr Puigdemont said: "It's a day of joy, not only for us, but all those who believe in a Europe founded on the will of its citizens.
"It's proof that it's worth fighting."
Mr Puigdemont and Mr Comin were elected to the European Parliament in May, but they were unable to take office because they are living in Belgium and did not attend a Spanish swearing-in ceremony.
Madrid has accused them of sedition for their role in helping organising a banned Catalan independence referendum in 2017.
Yesterday, the European Court of Justice ruled that MEPs enjoy parliamentary immunity from the moment the results are known, and they should have been able to take their seats.
If Spain wants to prosecute them, it must first make a case to parliament to strip them of this immunity.
Madrid has not yet done so, but the Spanish supreme court has given prosecutors and defence counsel five days to make their case before it responds to the European judgment.