When Johannes Melstvedt Østensjø was born on 6 October 1885, in Haugesund, Rogaland, Norway, his father, Torsten Bryngelsen Østensjø, was 42 and his mother, Siri Johannesdatter Melstvedt, was 37. He married Ruth Lothe on 30 April 1910, in Skåre, Rogaland, Norway. He died on 1 May 1964, at the age of 78, and was buried in Haugesund, Rogaland, Norway.