The 25-year-old becomes the latest addition to Andoni Iraola's squad and is expected to be available ahead of this weekend's clash with Wolves.
Adli arrives on the south coast after a standout spell in Germany, where he played a vital role in Leverkusen's historic 2023/24 campaign under Xabi Alonso. The German side went unbeaten in domestic competition, lifting both the Bundesliga title and the DFB-Pokal.
Adli contributed nine goals in 29 appearances across the two tournaments and finished as the top scorer in the DFB-Pokal, further cementing his reputation as a decisive attacking threat.
His influence was not limited to domestic football. Adli also featured in Europe, helping Leverkusen reach the Europa League final, where they finished runners-up.
Prior to his success in Germany, he made his mark in France with Toulouse, winning the Ligue 2 Player of the Season award in 2020/21 before securing his move to Leverkusen.
"I'm very proud first of all to play for a club like Bournemouth. I was looking at my next move and I felt like Bournemouth was the perfect place for me," said Adli, via the club's official website.
"The people around give me a lot of confidence here and I'm very impressed with the facilities. The people at the club are full of love, so I'm very happy and proud to play for Bournemouth and hopefully achieve good things."