Theobald joined Otto IV, Holy Roman Emperor, on 4 July 1214 at the Battle of Bouvines, where he was taken in prisoner in the rout.

Between 3 and 10 April 1217 (during the Champagne war of Succession) he searched for his problematic paternal uncle the bishop of Toul Matthew de Lorraine, found him on the path Void Parupt in Saint-Michel-sur-Meurthe, and killed him with a spear (implying a fight rather than a murder).

The weapon he used to kill the unruly bishop was apparently borrowed from Simon of Joinville, who was an ally during the Champagne war of Succession and probably also a friend.As duke of Lorraine, his chief seat was at the city of Nancy.

In accounts, the dukes of Lorraine are always referred to as extremely handsome and talented[6] and, based on Theobald's military adventures, it is not unlikely that he was brave.

The killing of his uncle Matthew, Bishop of Toul, does not reflect well on his personality, especially when such actions were considered particularly egregious in the Middle Ages.