Born in TA 2922 of the late-Third Age, Morwen Steelsheen was considerably taller than most of the Men in Middle-earth due to her Dúnedain and High-Númenórean heritage, a trait that was said to be inherited by a number of her descendants. Owing to her High-Númenórean heritage, Morwen lived in Belfalas, of the Prince of Dol Amroth's kin, and she was called Steelsheen due to her beauty, grace and pride. She later moved with her family to the flowery vales of Lossarnach. That was when she met Thengel, son of Fengel. Despite being 17 years younger than him, Morwen loved him, and they married in TA 2943 and had five children, including Théoden and Théodwyn (mother of Éomer and Éowyn).
While living in Gondor for some time with her family, she moved to Rohan as Thengel became king and she became the Queen of her husband's country. The people of Rohan came to like Morwen, and she was called Steelsheen because of her notable grace and height. Even after her husband passed away in TA 2980, it can be assumed that Morwen outlived her husband. The people of Gondor tended to lead longer lives than the Rohirrim, particularly the Gondorians who were descendants of the Númenóreans that survived the destruction of Númenor. Despite this, Morwen Steelsheen's date of death is not known.