The 34-year-old US citizen was making threats on social media towards the American singer-songwriter and her boyfriend Travis Kelce.
The man, who had a ticket to Swift's concert in Gelsenkirchen, was detained after being identified at the admission control point to the venue on Wednesday. The police investigation could not rule out that the man posed a threat to the iconic pop-star.
According to German police, he will remain in custody until Saturday of this week.
Wednesday's concert was one of three sold-out Eras Tour shows in the German city of Gelsenkirchen. Wednesday saw 60,000 'swifties' in attendance.
Ahead of the concert, people took to the streets to hang up signs renaming the city "Swiftkirchen". An offciall yellow sign with the new name was unveiled on Tuesday after a Taylor Swift fan petitioned the mayor to do so.
Mayor Karin Wedge thanked the teenager who proposed the "great idea" in her letter of acceptance.
The city is set to see 200,000 'swifties' over the three days.
After Gelsenkirchen, Swift will perform four more German shows in both Hamburg and Munich before travelling to Poland and Austria.
