Děpold I (also Děpolt, modern English Theobald) was a son of Vladislav I of Bohemia and brother of Vladislav II. He inherited Jamnitz (or Jemnice) as duke on his father's death in 1125.
In 1145, he joined the other territorial dukes of Bohemia, Conrad II of Znojmo, Vratislaus II of Brno, and Otto III of Olomouc, to attack Heny Zdika, bishop of Olomouc and chase him from his diocese. For this, Děpold was excommunicated. Subsequently, he went on a pilgrimage to Rome for atonement.
In 1147, while his elder brother Vladislav II went on the Second Crusade as far as Byzantium, Děpold governed Bohemia. He was ruled with a strong hand and prevented a seizure of power by the young Sobeslav. In 1153, he married Gertrude, daughter of Albert the Bear, Margrave of Brandenburg. Afterwards, he joined his brother-in-law on the warpath. In 1158, he went with the Emperor Frederick Barbarossa into Italy and was present at the siege of Milan. He would be the leader of several subsequent Bohemian expeditions to Italy. In 1167, he was joined by his nephew Frederick in leading a large force on behalf of King Vladislav. On that expedition, many noblemen died of an epidemic (possible plague or malaria), including Rainald of Dassel and Welf VII. Děpold was also among them.