The 24-year-old boyfriend, identified by police in Catalonia as the principal suspect in the case, has been arrested by French police, Catalan daily La Vanguardia reported.
His detention came after the body of the young French tourist was found at 12.30pm on Sunday by staff at Barcelona's Hotel Olivia Plaza. She was face down and covered in a bloody sheet. Her body displayed knife wounds.
A note was found and is currently being analyzed by investigators.
Catalan police have not ruled out any hypotheses in the case but the woman's boyfriend was named as the chief suspect after he fled to France.
The couple are thought to have travelled to Barcelona for the weekend, sources said.
Both the young woman and the young man had been reported missing by their families, with the families stressing the fragile psychological state of the woman.
She was depressed and had suicidal tendencies, the 19-year-old's family told police when filing a missing person's report.