Brynjólfur Bjarnason (26 May 1898 – 16 April 1989) was an Icelandic communist politician. He became a student at the University of Copenhagen, and in 1923 he became a communist during a stay in Berlin. After returning to Iceland, he became a teacher. In 1930 he became the chairman of the Communist Party of Iceland when it was founded.
Bjarnason attended the 2nd congress of the Communist International in 1920 and the 5th congress in 1924, as the representative of the Icelandic League of young communists. In 1935 he represented the Icelandic party at the 7th congress of the Communist International. In 1938 he became general secretary of the Popular Unity Party - Socialist Party (formed through the unification of communists and socialists).
After his retirement from politics he wrote several books on philosophy.