Ullmann's father is an actor who ran his own acting agency in Hamburg. His half-sister is a dancer, and his sister Shantia Ullmann is also an actress. As a result, Ullmann was already on stage at the Ernst Deutsch Theater in Hamburg at the age of eleven.
In 1996, he landed a role in the television series "Alphateam" under the direction of Norbert Schulze. Shortly thereafter, he appeared in the short film "Das Rennen" by Oleg Skworzow. After various guest appearances in television episodes, Ullmann received a recurring role in the series "Zwei Männer am Herd" in 1999.
