He was the youngest son of
Anne and
Rolf Thommessen, and thus a paternal grandson of
Ola Thommessen and maternal grandson of
Mikkel Dobloug. Together with Mimi Reimers (1906–1983) he had three sons, Rolf, (1930-2013), Henrik Peter Thommessen, (1931-2012) who married
Annette Thommessen and Mikkel, (1945-) Mimi Reimers was a granddaughter of
Herman Johan Foss Reimers and
August Geelmuyden Spørck. Later he married Ellen Thykier, (1919-2016) and had a daughter, Trine, (1950-2011). Ellen Thykier was Danish and the daughter of the sculptor Niels Rasmussen Thykier and the physician Ellen Marie Kruse, Through his sister Susanna, Olaf D. Thommessen was a brother-in-law of
Harald Hals. ==Career==