Colosimo was born in Melbourne, one of four children of Italian-born parents from Calabria. He grew up in the inner city suburb of Carlton North. He has a daughter, Lucia (2002), with his former wife, Actress Jane Hall. Colosimo and Hall worked together on A Country Practice in 1994. He lived in Westgarth, a suburb of Melbourne, until late 2015. The mother of his second child is Australian Actress Diana Glenn with whom he had a son, Massimo, in April 2014. The couple separated 2 months after the birth of Massimo.