Robert Sillberg studied at the Performing Arts School in Gothenburg. He made his musical debut in Mary Poppins at the Göteborg Opera where he has also performed in Guys and Dolls, Sunset Boulevard, West Side Story, La Cage aux Folles and The Phantom of the Opera.
At Chinateatern he performed in the comic musical The Book of Mormon and at the Oscarteatern in La Cage aux Folles. At Malmö Opera, Robert Sillberg has appeared in Beauty and the Beast and at Kulturhuset Spira in Jönköping performed in the Broadway musical On the Town and Camera, the musical about Ingrid Bergman's life.