She was the daughter of the noble, council and governor Jørgen Marsvin and Karen Gyldenstierne. She was married to Ludvig Munk in 1589. Widowed in 1602, she married the governor and noble Knud Rud in 1607. She was twice widowed in 1611.
In 1615, her only child, Kirsten, married the king; Ellen had demanded that her daughter be married and not the mistress of the king, and she also formed the marriage contract, in which it was stated that Kirsten should be the legal spouse of the king and receive a county as widow pension. Ellen was made the guardian of her daughters children with the king and the trustée of the allowances given to her grandchildren and made responsible for their fortune. She was made county administrator of Dalum Kloster 1620 (until 1639), unusual for her gender in the 17th century.
Marsvin was one of the most successful landowners in Denmark: by her inheritance, money and connections, she bought, sold and built large estates with great success, and was in 1625 one of the richest landowners in Denmark.
In 1629, when her daughter was accused of adultery, she introduced the king to his next lover, Vibeke Kruse; to justify Kirsten's adultery, or to keep her personal influence over the monarch. The king respected her for her skill as a businessperson. In 1639, however, the king grew tired of her persistent demand that he recognize his wife's youngest daughter Dorothea Elisabeth, (her own youngest grandchild) as his, and as a result, he fired her as county administrator. She left court and lived the rest of her life at her estates.