The 19-year-old, who initially joined the Bundesliga club on a two-year loan deal in summer 2014, has signed a contract at the BayArena until 30 June 2020.
'The best option'
"Tin Jedvaj has great potential and has consistently shown that in the few months he's been at Bayer 04," explained Leverkusen sporting director Rudi Völler. "His versatility is a real plus for us, so why we decided to wrap up the deal as soon as we could."
An equally delighted Jedvaj, who was recently voted Croatia's most promising youngster and has made 17 appearances in all competitions so far this season, scoring twice and chipping in with one assist, said: "Bayer 04 are the best option for me and good for my development. I really want to get stuck in at Leverkusen."