Theobald I (French: Thibaut or Thibauld de Bar) was the count of Bar from 1190 until his death, and a count of Luxemburg from 1197 until his death. He was the son of Reginald II of Bar and his wife Agnès de Champagne. He became count when his brother, Henry, was killed in the Siege of Acre.
After his third marriage, he sought to reclaim his wife's lands of Luxembourg, Durbuy and Laroche with the approval of Philip of Swabia. Theobold therefore besieged the castle at Namur, whereupon a conference was held in which Philip of Namur and his brother Baldwin renounced the disputed territories of Luxembourg, Durbuy and Laroche. The Treaty of Dinant signed 6 July 1199 at Saint Medard, later made it official.
After his death in 1214, his eldest son Henry II, from his second marriage; succeeded him as count. His eldest daughter Agnes, from his first marriage, married Frederick II, Duke of Lorraine. His lands in Luxembourg reverted to Waleran III of Limburg, who married Theobald's widow Ermesinde of Namur. Theobald was buried at St. Mihiel.