Grbic, 23, has signed a five-year contract in a deal that is expected to top €10m.
The Ligue 2 champions announced the signing with a video showing Grbic jumping out of a plane.
🪂 Nouveau joueur en approche : opération aéroportée en cours pic.twitter.com/Tg32LXbgbm
— FC LORIENT 🐟 (@FCLorient) July 8, 2020
Lorient beat Brest to the acquisition of Grbic, a prolific goal scorer in the second level of French football.
Brighton, Celtic and Rangers were also interested in taking the young striker to the British Isles.
In the 2019-20 season, Grbic finished with 17 goals, behind only Le Havre’s Tino Kadewere in the rankings.
During his youth days, Grbic was on the books of Austria Vienna and VfB Stuttgart.