Michael Donnellan was born in Dublin and trained as a surgeon before making the move from medicine to fashion. After wartime service, he joined the fashion house of Lachasse as chief designer – he was named head of its operation from 1941. In this role at Lachasse, he was following in the footsteps of two other great London couturiers – Digby Morton and Hardy Amies. Although he was attached to a large and respected fashion house, he was already a name in his own right – Michael of Lachasse – and was included among London's "big 10" in a feature in "Life" in 1953 about the run up to the coronation of Elizabeth II.