The Irish actress, 30, was photographed sitting in 34-year-old Cooper's lap with her arms wrapped around him as they soaked up the sun on the island of Ischia, reported Contactmusic.
The couple shared passionate kisses and laughed while clambering onto the same sun lounger.
Cooper was first linked to Negga after they both starred in West End play 'Phaedra' in 2009, but the actor had then reconciled with his "Mamma Mia!" co-star Amanda Seyfried.