Crowds watched as the 21-year-old British free climber made his way to the top of the 381-ft Melia Barcelona Sky Hotel in the Spanish city. King scaled the Barcelona hotel in about 20 minutes.
As he was coming down, he was arrested by the Mossos d'Esquadra, the Catalan regional police and faces a fine.
"When I was at the top I felt that I was in another dimension of bliss," King told Reuters. "When I met the police on the way down my head was still in the clouds."
He first climbed the 1,017-ft Shard building in London in 2019, the highest tower in the United Kingdom, without any safety apparatus.The feat earned him six months in a young offenders' centre for breaching a civil injunction taken out by the owners of the building.
King, from Oxford in England but currently travelling around Europe in a van, has also climbed the 474-ft Agbar Tower skyscraper in Barcelona.