Reared in Romania, Dornhelm emigrated to Austria in 1960 where he studied film and TV at the University of Vienna. He spent most of the 1960s and 70s directing documentaries for Austrian TV. "The Children of Theatre Street" (1977), a documentary about the Kirov Ballet School, narrated by Princess Grace of Monaco, earned an Oscar nomination. Dornhelm returned to the subject to profile ballet dancer Kyra Nijinsky in "She Dances Alone" (1981). The following year, he worked on the short film "Rearranged" which would have marked the return to acting of Grace Kelly (Princess Grace of Monaco) had her untimely death not left the project unfinished. Dornhelm profiled rock musician Bill Wyman in "Digital Dreams" (1983).
Having moved into fictional features, Dornhelm has continued with "Requiem Fur Dominic" (1990), a semi-autobiographical story about a Romanian-born Austrian who returns to his boyhood home to find that his best friend is accused of 80 murders. His "A Further Gesture" (1997), featuring Stephen Rea, focused on an Irish Republican Army gunman who breaks out of prison to begin a new life in New York.
Dornhelm has ventured into American TV with "Fatal Deception: Mrs. Lee Harvey Oswald" (NBC, 1993), which explored the marriage of the accused assassin of President John F. Kennedy (Frank Whaley) and his Russian-born wife Marina (Helena Bonham Carter).