Theobald I (French: Thiébaud or Thiébaut) (c. 1191 – February 17, 1220) was the duke of Lorraine from 1213 to his death. He was the son and successor of Frederick II and Agnes of Bar.
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. He was quickly liberated.
In 1216, in the Champagne War of Succession, he supported Erard I, Count of Brienne, in his quarrel with Theobald IV, Count of Champagne, who was supported by Philip II of France, Frederick II, Holy Roman Emperor, and Henry II of Bar. Frederick, the suzerain of Lorraine, considered it a felony to support a candidate he opposed and occupied the city of Rosheim, which he had given to Frederick II of Lorraine. Theobald responded in 1218, retaking Rosheim and ravaging Alsace. Frederick did not hesitate to counterattack and invaded Lorraine and took and burned Nancy, its capital. He then besieged and took the castle of Amance, where Theobald was taking refuge. He was imprisoned and constrained to recognise the suzerainty of the count of Champagne, the legitimacy of Erard of Brienne's claim to Champagne, and relinquish several lordships to attain liberty again. He never recovered his lost land and prestige and died in 1220.
He had married, in 1206, Gertrude, only child and heir of Albert II, count of Dagsburg and Metz. They had no children. His successor was Matthias his brother; his widow remarried his old rival, Theobald of Champagne.