Paul Isberg was a navy career officer and rose to the rank of captain. For some time he served as a recruiting officer in Stockholm. During World War II he accompanied Swedish charter vessels to South America. He was appointed Knight of the Order of the Sword, the Danish Order of the Dannebrog, Prussian Order of the Crown and of the Red Eagle.
Isberg married Astrid Emma Christina (née Ehrnberg) in 1908. The couple had one daughter and three sons. After divorce, he married his second wife in 1939. With Sonja Margit (née Danielsson), 32 years his junior, he had one more child. He was a member of the crew of the Swedish yacht Kitty, which easily won both races in the 10-metre class at the 1912 Olympic Games. Kitty and her crew won the first Swedish gold in sailing.