Ubertus became bishop of Chiusi in 1146.

Noonan, "Gratian Slept" 153-154: "While his abbatial title is only slightly older than his Camaldolese habit, Gratian has been recognized as a bishop since the twelfth century. The Chronicon of Robert de Torigny abbot of Mont-Saint-Michel, writing sometime between 1162 and 1184, identifies Gratian positively as 'episcopus Clusinus' or bishop of Chiusi .  .  .  <fn>Anonymous, Gloss on MSS of Concordia discordantium canonum: Ghent, Bibl. Commun, et Univ. 55; Paris B.N. 3884; Trier 906; Mazarine 1289; Rouen 707; Montecassino 66; Pommersfelden 2744; London, Beatty 46, all as reported in <Kuttner> Repertorium, 14."

This scenario (i.e. Gratian's episcopal office ca. 1143) would fit well with what we may learn about Gratian from the Decretum itself. He would have taught the first recension in Bologna at least during the first years of the 1140s. Perhaps he only taught the Decretum once. Indeed, the work as it appears in the first recension looks unfinished, since it does not treat baptism, confirmation, and the consecration of churches, subjects which one would think would have interested the practical theologian Gratian. Did he become bishop before he had finished his course the first time he taught it? There is no reason to assume, as is often done, that Gratian must necessarily have had a very long teaching career. Indeed, as nobody in the schools remembered very much about him, there might be good reasons to assume that his teaching career was rather short.

Anders Winroth, "Where Gratian Slept: The Life and Death of the Father of Canon Law,"  Zeitschrift der Savingy-Stiftung für Rechtsgeschichte, Kan. Abt. 99 (2014) 105-128 at 125-126.