Brolly was born in Belfast, Northern Ireland, and comes from a family of Irish actors, although he has done most of his film work in the United States. After some independent films, he played a small role in the science fiction thriller Impostor, based on a story by Philip K. Dick. His most notable role to date is in Underworld as Kraven. He reprised the role for Underworld: Evolution and Underworld: Rise of the Lycans. He starred in CSI: NY in 2007 in the final episode of Season 3 "Snow Day". Besides acting, Brolly writes and directs films. His first short film, Y's Guys, was well received at the Atlanta, New York and Daytona Beach film festivals.