[2] Born in Helsinki, Ehrnrooth first went to Svenska normallyceum i Helsingfors and then entered cadet school in 1922 and served in the Uusimaa Dragoon Regiment (Uudenmaan Rakuunarykmentti).

In 1958 he married a Danish countess Karin-Birgitte Schack who was a lady-in-waiting and a close friend of Queen Ingrid of Denmark.

When the Continuation War, also against the Soviet Union, broke out in June 1941, he served as the chief of staff of the 2nd Division until he was seriously wounded.

The long post-war era during which it simply was not progressive to value the military ended in the early 1990s, at which time his charismatic persona was at its height.

In his last statement he gave support to ProKarelia (Finnish NGO) and its plan for the Return of Ceded Territories.