The 26-year-old has signed a five-year contract with Leverkusen and joins the club for a reported fee of €11.5million.
Aranguiz turned down moves to the likes of Arsenal, Chelsea and Leicester to join Leverkusen.
“I picked Leverkusen because they always showed interest in me,” Aranguiz said.
“No other club talked to me. They were always very clear.”
— Bayer 04 Leverkusen (@bayer04fussball) August 13, 2015