Kai Birger Knudsen (25 June 1903 – 3 March 1977) was a Norwegian judge and politician for the Labour Party.
He worked as an auditor in Haugesund 1926-1927, then deputy judge for the Heddal District Court from 1928-1930, and junior solicitor in Notodden Municipality 1930-1935.
As an elected politician he served in the position of deputy representative to the Parliament of Norway from the Market towns of Telemark and Aust-Agder counties during the term 1945–1949.
[2] During Torp's Cabinet Knudsen became acting Minister of Justice and the Police from 18 October 1952 to 20 December 1952, then on a permanent basis until 15 June 1954.
In the new Gerhardsen's Third Cabinet Knudsen was appointed Secretary to the Prime Minister again, but left in late 1955.