Sondermajer was born in Czernowitz, capital of the Duchy of Bukovina, Austrian Empire (present-day Chernivtsi in Ukraine), a son of Franciszek Sondermeier, native of Bavaria, and a Polish mother.
He had a brother called Adam.
He finished high school in Lviv and received his medical degree in 1884, from the Polish Jagiellonian University in Kraków, specialising in surgery.
After graduating he worked as assistant professor, in the Department of Surgery, under Professor Jan Mikulicz-Radecki.
  
In 1889, recommended by Dr. Mikulicz-Radecki, and at the invitation of Serbia's Chief of Medical Staff, Colonel Dr. Mihailo Marković, Dr. Sondermajer left Kraków for Serbia.
He is immediately admitted to the Army Medical Service with the rank of Captain, his first duty is to set up the Surgical Department at Belgrade Military Hospital, he became director of the hospital as well as head of the surgery department, a position he kept from 1889 to 1910.
 
Dr. Sondermajer initiated the construction of a new military hospital in Vračar, the works started in 1903, he personally oversaw and controlled the construction.
In 1905 he became Colonel.
In 1909, with the new building finished, he became the chief of the hospital.
At the time it was the most modern hospital in Serbia.
Sondermajer was born in Czernowitz, capital of the Duchy of Bukovina, Austrian Empire (present-day Chernivtsi in Ukraine), a son of Franciszek Sondermeier, native of Bavaria, and a Polish mother. He had a brother called Adam. He finished high school in Lviv and received his medical degree in 1884, from the Polish Jagiellonian University in Kraków, specialising in surgery. After graduating he worked as assistant professor, in the Department of Surgery, under Professor Jan Mikulicz-Radecki.   
In 1889, recommended by Dr. Mikulicz-Radecki, and at the invitation of Serbia's Chief of Medical Staff, Colonel Dr. Mihailo Marković, Dr. Sondermajer left Kraków for Serbia. He is immediately admitted to the Army Medical Service with the rank of Captain, his first duty is to set up the Surgical Department at Belgrade Military Hospital, he became director of the hospital as well as head of the surgery department, a position he kept from 1889 to 1910.  
Dr. Sondermajer initiated the construction of a new military hospital in Vračar, the works started in 1903, he personally oversaw and controlled the construction. In 1905 he became Colonel. In 1909, with the new building finished, he became the chief of the hospital. At the time it was the most modern hospital in Serbia.
Roman Sondermajer