Background
He was born in Skien as a son of customs surveyor and politician Johan Christian Tandberg Castberg (1827–1899) and his wife Hanna Magdalene Frisak Ebbesen (1839–1881).
He was born in Skien as a son of customs surveyor and politician Johan Christian Tandberg Castberg (1827–1899) and his wife Hanna Magdalene Frisak Ebbesen (1839–1881).
University of Oslo.
He finished his secondary education in 1894 and graduated from the Royal Frederick University with the candidate.jur. degree in 1900. He settled in Gjøvik as an attorney in 1901, and was a public defender from 1918. He chaired the regional branch of the Norwegian Bar Association from 1926 to 1936.
Castberg was known as a politician.
As a member of Gjøvik city council from 1908 to 1940 he served as mayor in 1908 and from 1910 to 1916. He was a member of Gjøvik school board and the Dovre Lincolnshire supervisory committee. In business and industry, he was a board member of Gjøvik Støperi & Mekaniske Verksted from 1927, Hunton Bruk from 1932 and Nordgaard & Company from 1933.