Magasiva is the first son of Salafa and Taufaiula Ropati Magasiva, he has four brothers, Stevan, Miki, twins Pua and Tanu, and adopted sister Trina Magasiva. He inspired his younger brother (Pua) to become an actor, landing him an audition for an alcohol awareness commercial. Pua died aged 38 on 11 May 2019. As a result, Robbie Magasiva flew to Wellington to be with his family. Later he opened up about the devastating loss of his brother and raised mental health awareness.