Theodoric III of Nassau-Wiesbaden-Idstein (German: Dietrich III. von Nassau-Wisebaden-Idstein) (c. 1250 - 22 November 1307) was the Archbishop of Trier from 1300 until 1307.

Theodoric was a son of Count Walram II of Nassau-Wiesbaden-Idstein and Adelaide of Katzenelnbogen. In 1292 he joined the service of his brother, King Adolph I, but after his death in 1298 at the Battle of Göllheim it was decided that Theodoric would be a churchman instead. Theodoric became a strong supporter of the Dominican Order, and became a member of the Cathedral at Trier. After the death of Bohemond I of Warnesburg in 1299, the cathedral chapter elected Henry of Virneburg archbishop, but Pope Boniface VIII instead for political reasons appointed Theodoric the archbishop in 1300.

Theodoric's reign was marked byn conflicts. The city of Trier was near bankrupt, and the other cities in the electoral principality were struggling for greater rights and privileges, and in 1304 he violently brought Coblenz to heel and banned the city from ever having a town councillor. Theodoric also had conflicts within the church. He confiscated the income of the parish churches, and in 1303 ordered the cathedral chapter pay concessions. He also stole the holy relics of the cathedral, and the Abbeys of St Simeon, St Paul and St Maximin, and placed them in his private residence. The abbeys in 1306 appealed to the Pope, but Theodoric died the following year in Trier before he could be deposed and excommunicated.

Preceded by:

Theodoric III of Nassau-Wiesbaden-Idstein

Succeeded by:

Bohemond I of Warnesburg Archbishop of Trier
1300 - 1307
opposed... Henry III of Virneburg
1300 - 1306
Baldwin of Luxembourg