She succeeded suo jure to the title of Countess of Soissons upon the death of her father, Enguerrand VII de Coucy, on 18 February 1397.

When Marie was about a month old, she accompanied her parents to England, where on 11 May 1366 her father received the title of Earl of Bedford and was inducted into the Order of the Garter.

Upon Enguerrand's death on 18 February 1397 in a Turkish prison at Bursa, Anatolia, five months after the ferocious Battle of Nicopolis, Marie inherited his title and became the suo jure Countess of Soissons.

[3][4] In October 1397, on the lengthy journey home to France, Henry of Bar died at the Crusaders' camp in Treviso after having contracted the plague during his sojourn in Venice.

The rich barony was described as "having castles of grandeur, with its 150 towns and villages, its famous forests, fine ponds, many good vassals, much great nobility and inestimable revenues".