Marta Steinsvik (23 March 1877 – 27 July 1950) was a Norwegian author and translator. She was a champion of women's rights and promoter of the use of Nynorsk. She was the first female to graduate from the Norwegian School of Theology. 
Steinsvik was born in Flekkefjord. he studied medicine in Kristiania, but never finished her studies because she was against vivisection. She studied several other subjects including Egyptology in London. In 1902, Marta Steinsvik studied oriental languages including Assyrian and ancient Egyptian. She also became interested in Esotericism. She was influenced by the thinking of both English Theosophist, Annie Besant and Austrian philosopher, Rudolf Steiner. She was the first woman to graduate from the Norwegian School of Theology, but was not allowed to practice. She was the first Norwegian woman to preach in a church, during 1910 at the Grønland church in Oslo. She was invited to an international women's conference in Geneva, and planned to give a talk on women priests, until the Pope forbade all Catholic women to attend if she did, forcing her to give a speech on another subject.
In 1894 she started writing in the newspaper, Den 17de Mai, which had been started that same year by her future husband Rasmus Steinsvik. She was employed as secretary to Hans Tambs Lyche, editor and founder of the cultural journal Kringsjaa'. In 1910 she became editor of the paper Kringsjaa. She was multilingual and translated several books into Nynorsk, including Personal Recollections of Joan of Arc, by the Sieur Louis de Conte written by Mark Twain and Quo vadis? written by Henryk Sienkiewicz.
Marta published Frimodige ytringer, ("Frank Speech") in 1946. It was about the Norwegian treatment of suspects when they were punishing traitors after the Second World War. The book includes examples of Norwegian resistance movement torturing suspected Nazi sympathizers in the summer of 1945. It also discussed the legality of withdrawing a group's human rights, (those who were members of Nasjonal Samling, the Norwegian National Socialist party, after 9 April 1940), by an ex post facto law that set aside the Hague Convention which Norway had ratified.
The papers left behind on her death are currently being organised at the Norwegian cultural institution, The Blue Colour Works. Several people have announced their plans to write a book about Marta Steinsvik.
- Ægteskabet og forplantningen, 1910
- Gammelægyptiske mysterie-indvielser, 1917
- Bispen: eit sjæle-drama i 3 akter, 1918
- Isis-sløret: mysterie-drama i 5 akter, 1921
- Sankt Peters himmelnøkler, 1928
- Hellig Olav og Den norske statskirke, 1930
- Kvinner som prester, 1934
- Frimodige ytringer, 1946
She was born Marta Tonstad on the farm Skjeggestad in Bakke ( now part of Flekkefjord) in the county of Vest-Agder, Norway. Both of her parents Torkild Tonstad (1852–1908) and Ingeborg Evertsdatter Haugan (1848–1922) came from old farming families. Her father worked as a teacher in Flekkefjord and owned the farm Skjeggestad, where Marta lived until she was three years old.
On 16 May 1896, she married Rasmus Steinsvik (1863–1913), the founder and editor of Den 17de Mai. She had problems in childbirth and her doctor told her a sixth child would be likely to kill her, so she moved away from her husband. Her husband had a friend who was a doctor who diagnosed her as insane as soon as he heard she believed in reincarnation, and her husband had her committed. While institutionalized, she took the opportunity to study psychology. Another doctor became interested in her case and was able to get her released. This episode was often later used against her in newspaper debates. Her husband died in 1913 after an operation, barely 50 years old.