Marie Sophie Schwartz, née Birath (4 July 1819 in Borås - 7 May 1894), was a Swedish writer. She is counted as among the most noted and popular of her time in contemporary Sweden.
She was the illegitimate daughter of a maid, Carolina Birath, and the foster daughter of the customs official Trotzig in Stockholm. Wealthy relatives provided her with an education by placing her in a girl's school. From 1840, she lived with the professor Gustaf Magnus Schwartz, who was married to a Catholic and therefore could not marry her. She debuted under the pseudonym Fru M.S.S. (Mrs M.S.S) in 1851. In her work, she participated in the public debate, criticized social snobbery and supported women's emancipation. Her works was translated to Danish, German, French, English, Dutch, Hungarian and Polish.