Kai Birger Knudsen (25 June 1903 – 3 March 1977) was a Norwegian judge and politician for the Labour Party. He was born in Vardø as a son of kemner Kai Angell Knudsen (1869–1944) and Julie Huse (1873–1952). He finished his secondary education in 1922, and graduated with the cand.jur. degree in 1926. He worked as an audit in Haugesund 1926-1927, then deputy judge in Heddal 1928-1930 and junior solicitor in Notodden 1930-1935. After the war he was acting district stipendiary magistrate (sorenskriver) of Tinn and Heddal from 1945 to 1946, and also mayor of Notodden during the same period. 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. He then worked in