Rabbat was born in Beirut, Lebanon in 1960. He lived in West Beirut up until the Lebanese civil war, when in 1976 he had to flee with his family to East Beirut. He studied at the Christian Brothers schools and graduated from Ashrafieh High School in Lebanon. In 1979 he came to the United States to study engineering at Ohio State University. In 1982 he graduated from OSU with a B.A. on Engineering and a B.A. in Mathematics.