Brynild Anundsen was born in Skien in Telemark county, Norway. Anundsen immigrated to the United States during 1864 settling first into La Crosse, Wisconsin. Anundsen served as a private in the Union Army during the American Civil War between 1864 and 1865.
Anundsen, who had learned the printers trade in Norway, worked for the Norwegian language newspapers Emigranten in Madison, Wisconsin and Fædrelandet og emigranten of La Crosse, Wisconsin. In 1867 he moved to Decorah, Iowa where he established Ved Arnen, a Norwegian language literary magazine in 1866 and a newspaper, Fra Fjærnt og Nær in 1869.
On September 18, 1874, Anundsen started Decorah Posten. It was a well-edited newspaper, its size and familiar format developed gradually. The publisher avoided areas of political and religious controversy, which had destroyed so many earlier papers. Anundsen made a success of the Decorah Posten and went on to establish the Anundsen Publishing Company. Anundsen was a founder of the Norwegian Society in America (Norwegian: Det Norske Selskab i Amerika). In 1895, he was chosen president of the Norwegian-Danish Press Association of the United States.
In 1865, Anundsen was married in La Crosse, Wisconsin, to Esther Mathilde Charlotte Hofstrom, a native of Sweden. She died during 1899. Following the death of his first wife, he married Helma Beatha Hegg in 1901. In 1906 he represented the state of Iowa at the coronation of Haakon VII of Norway and Queen Maud and was made a Knight First Class of the Royal Norwegian Order of St. Olav by King Haakon VII. Anundsen was an active member of the United Lutheran Church of Decorah.
- Anundsen, Brynild (Winneshiek County IA Lutheran Cemetery)
- B. Anundsen, Biographical (Past and Present of Winneshiek County, Iowa. Volume II. pages 5-7. 1913) 
- Brynild Anundsen, Publisher of the "Decorah-Posten" Norwegian-American newspaper (The Promise of America. National Library, Oslo) 
- Decorah-Posten: The Story of an Immigrant Newspaper (Odd S. Lovoll, Norwegian-American Historical Association. Volume 27: Page 77) 
- Norsk-Amerikanernes Festskrift 1914 (The Promise of America)
- The Biographical Dictionary of Iowa (The University of Iowa Libraries) 
- Øverland, Orm The Western Home: a literary history of Norwegian America (Norwegian-American Historical Association. 1996)
- Andersen, Arlow W. Rough Road to Glory: The Norwegian-American Press Speaks Out on Public Affairs, 1875 to 1925 (Balch Institute Press. 1990)
- Bailey, Edwin C. Past and present of Winneshiek County, Iowa: A record of settlement, organization, progress, and achievement (1913)
- Nelson, O. N. History of the Scandinavians and Successful Scandinavians in the United States ( O.N. Nelson & Co. 1904)