The 32-year-old centre-back, who spent the back end of last season out on loan with Russian side FC Anji Makhachkala, will link up with his new teammates on 4 July.
On the radar
"In Emir Spahic, we've been able to sign a central defender with a great amount of international experience," said Leverkusen's CEO Wolfgang Holzhäuser. "We have known about him for many years [...] We're convinced that we've got a very strong central defence now with Philipp Wollscheid, Ömer Toprak and Emir Spahic."
Bayer's director of sport Rudi Völler added: "Emir Spahic is strong technically and strong in the tackle. He's also tactically well-versed and good in the air. He's going to help us reach our goals in the Bundesliga, the DFB Cup and, of course, also in the UEFA Champions League."
Spahic, the cousin of former VfL Wolfsburg striker Edin Dzeko, has already appeared in the Champions League once for NK Zagreb, alongside current Wolfsburg striker Ivica Olic, and also has Europa League experience with Montpellier Hérault SC, Sevilla and Lokomotiv Moskva.