The Chronicon Sancti Michælis, monasterii in pago Virdunensi names "Theodoricus" son of "Frederico". "Adalberonem filium Beatricis nobilissimæ ductricis, matris Theoderici ducis" is named in the Gesta Episcoporum Virdunensium. The Chronicle of Alberic de Trois-Fontaines names (in order) "ducem Theodericum et…Alberonem episcopus" as sons of "Fridericus dux Mosellanorum" & his wife Beatrix. The Gesta Episcoporum Virdunensium names "Theoderici ducis Barrensis" son of "ducis Frederici et Beatrici, Hugonis Capitonis Francorum regis soror".
He succeeded his father in 978 as THIERRY I Duke of Upper Lotharingia, under the regency of his mother until 987. Lothaire King of France invaded Upper Lotharingia again in 983, advancing as far as Brisach where he was forced to retreat by Swabian troops. The French king returned to Lotharingia in 985 and besieged Verdun, where in Mar 985 he captured Duke Thierry but released him in mid-985 through the intervention of the duke's mother and her brother Hugues Capet. Comte Héribert I [de Vermandois] captured the château of Stenay in Lotharingia in 987. In 1011, Duke Thierry was seriously wounded in an ambush at Odernheim, captured by Friedrich Graf [im Moselgau] [Luxembourg], and taken to Metz but released in return for hostages. "Heinricus…Romanorum imperator augustus" renewed the privileges of Kloster Fulda by undated charter, placed in the compilation with other charters dated 1020, witnessed by "Godifridi ducis, Berinhardi ducis, Thiederici ducis, Welphonis comitis, Cunonis comitis, Kunrati comitis, Ottonis comitis, Adilbrahtis comitis, Bobonis comitis, Friderici comitis, Bezilini comitis, Ezonis comitis palatini", the order of witnesses presumably giving some idea of the relative importance of these nobles at the court of Emperor Heinrich II at the time.
The necrology of Gorze records the death "III Id Apr" of "Theodericus dux". 1