Otto Bahr Halvorsen (28 May 1872 – 23 May 1923) was a Norwegian lawyer and politician from the Conservative Party, who served as the prime minister of Norway from 1920 to 1921 and again in 1923 up until his death in office.

He studied law at the University of Kristiania where he completed his examen artium in 1890.

[2] In 1912 Halvorsen was first elected to the Storting from the neighborhood of Gamle Aker in the district of St. Hanshaugen in Kristiania.

Between these terms, Halvorsen was leader of the Conservative Party in Parliament and President of the Storting (stortingspresident).

[3][4] However, he became gravely ill in March 1923, just a few days after forming his government, and died of cancer on the 23rd of May that same year.