Leif Castberg (23 April 1876 – 3 March 1950) was a Norwegian lawyer and politician for the Radical People's Party and the Conservative Party.

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).^[1] He had several brothers and sisters,^[2] including the politician Johan Castberg and violinist Torgrim Castberg.^[3]

Through Johan he was an uncle of law professor Frede Castberg, and through Torgrim he was an uncle of illustrator Johan Christian Castberg. He was a first cousin of sculptor Oscar Ambrosius Castberg, and his paternal grandfather Peter Hersleb Harboe Castberg was a priest and politician.^[3] On the maternal side he was a grandson of Jørgen Tandberg Ebbesen and nephew of Just Bing Ebbesen,^[4] both of whom were involved in politics too.

In 1900 he married Sigrid Flood; the marriage lasted until 1913. From 1921 he was married to Else Lingjerde.^[1]

He finished his secondary education in 1894 and graduated from the Royal Frederick University with the cand.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.^[1]

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 Line supervisory committee. In business and industry, he was a board member of Gjøvik Støperi & Mekaniske Verksted from 1927, Hunton Bruk from 1932 and Nordgaard & Co from 1933.^[1][5]