Knut Sejersted Selmer (7 November 1924 – 25 March 2009) was a Norwegian legal scholar. He was born in Aker as a son of professor Ernst Westerlund Selmer (1890–1971) and Ella Sejersted (1895–1968), and was the brother of Ernst Sejersted Selmer. He was a grandnephew of and Jens Selmer and a first cousin of Francis Sejersted. He finished his secondary education at the Haagaas School in 1944 and graduated with the cand.jur. degree in 1949. He was a deputy judge in Nord-Troms and Fredrikstad between 1949 and 1952. In January 1950 he married Elisabeth Schweigaard.