Material found in Harley MS 3859
The earliest material giving evidence of Urien is to be found in Harley MS 3859, a manuscript copied c. 1100 in Saint Augustine's, Canterbury, or in an associated centre, possibly even across the Channel. Together with various Classical texts, it contains the Harleian genealogies as well as a copy of the Historia Brittonum (written in 829-30 in Gwynedd) and the Annales Cambriae. This manuscript is celebrated among Welsh manuscripts because of its early date and the material concerning the early Middle Ages found within it. The Welsh material in Harley 3859 probably was compiled together in the exemplar of this manuscript, which was most likely written around 954 at St Davids in the reign of Owain ap Hywel Dda. The genealogies were probably first composed before 872 in Gwynedd at the court of Owain's ancestor Rhodri Mawr to support the legitimacy of this dynasty to rule over Gwynedd and the Isle of Man.
Urien's genealogy in Harley MS 3859 gives his patrilineal descent as "Urien son of Cynfarch son of Meirchion son of Gwrwst son of Coel Hen." His earliest recorded ancestor, Coel Hen, functioned as an origin point for many of the northern Brittonic-speaking dynasties of the early Middle Ages in northern Britain. In modern scholarship, it is not generally held that Coel was an important historic figure or truly the ancestor of all these families, especially those extraneous dynasties given descent from him in the much later fifteenth century genealogical tracts titled Bonedd Gwŷr y Gogledd. Since the "Coeling" first appear in genealogies together in Harley MS 3859 with the Historia Brittonum, which narrates the end of Urien's career, it is thought the compiler of the genealogies joined together the lineages of all the Brittonic-speaking leaders mentioned in the Historia Brittonum to add context to the narrative. Nothing is known of Urien's father Cynfarch, though he may have ruled over Rheged since later material makes reference to the family of the Cynferchyn (i.e., descendants of Cynfarch), which suggests he was important enough to be treated as an ancestor-figure.
Contra ill[os] quattuor reges, Urbgen, et Riderchhen, et Guallauc, et Morcant, dimicaverunt. Deodric contra illum Urbgen cum filiis dimicabat fortiter. In illo autem tempore aliquando hostes, nunc cives vincebantur, et ipse conclusit eos tribus diebus et tribus noctibus in insula Metcaud et, dum erat in expeditione, jugulatus est, Morcanto destinante pro invidia, quia in ipso prae omnibus regibus virtus maxima erat instauratione belli.
Against them [i.e. Hussa and his predecessors] four kings fought: Urien, and Rhydderch Hen, and Gwallog, and Morgan. Theodric used to fight bravely against that Urien with his sons, yet at that time sometimes the enemies, sometimes the citizens used to be vanquished. And he [Urien] shut them [the enemies] up for three days and three nights in the island of Lindisfarne and, while he was on [this?] campaign, he was slain at the instigation of Morgan out of jealousy, because beyond all other kings he [Urien] had the greatest skill in renewing war.
The Historia Brittonum is our only "historical" record of Urien, though its usefulness for reconstructing history is often doubted, as it was compiled and adapted hundreds of years after Urien's death from various sources. Interestingly, in a later prologue attached to the text, the author of the Historia Brittonum claims to have assembled his text based on the work of Rhun, Urien's son, who is also credited with baptising Edwin of Northumbria in 637, together with (or identical to) Paulinus of York, though the existence of Rhun's text is debated. Based on Bede and a Northumbrian source David Dumville called "the Anglian collection of royal genealogies and regnal lists", the text synchronises Urien's life to the reign of Theodric (r. 572-579) and Hussa of Bernicia (r. 585-92).
In this narrative, Urien took hostile action against Theodric, together with Rhydderch Hen, Gwallog ap Llênog, and Morgan, who are (excluding Rhydderch) all recorded as descendants of Coel in the genealogies contained in the same manuscript. The meaning of "with his sons" in the second line is also problematic, as it is uncertain whether this line refers to Urien's sons, or those of Hussa, though it is generally understood that those of Hussa are intended. Echoing Gildas, it is said that the conflict between the Britons and the Saxons went back and forth, but Urien and his allies eventually gained the upper hand and besieged Theodric on Lindisfarne (Old Welsh: Medcaut). Urien was killed at the instigation of Morgan, who, according to the author of the Historia Brittonum, was jealous of Urien's martial ability. As Morgan is supposed to have come from Bernicia, a nearby territory to Lindisfarne, it has been suggested that Morgan at that moment felt more as threatened by Urien's powerful presence near his home than by the weakened Theodric.
Hussa (not just Theodric) is directly described as Urien's foe in the first sentence, which leads to difficulties of interpretation. Kenneth Jackson suggested this meant either that Urien fought against Theodric and Hussa before the latter's reign or that the chronology here is wrong and that the narrative refers to the reigns of Ida's sons in general. Ian Lovecy understood the reference to Theodric as a long parenthesis indicating that formerly the struggle went both ways, but not in Urien's last campaign against Hussa. David Dumville understood the text to refer to the warfare of all four British kings against the five English kings previously named in the Historia Brittonum besides Hussa, that is, from the reigns of Adda to Hussa. The next king is Æthelfrith, who took the throne c. 593, and so Urien could even have died as late as this. However, the section of the Historia Brittonum preceding this narrative records the Christianisation of Kent (occurring in 596-7) as occurring in the reign of Frithuwald (reigned 579-85), implying Urien's campaigns could even have been after 597. This is one of many places in the Historia Brittonum with a confused chronology. For this reason, Patrick Sims-Williams cast doubt on the reliability of the chronology concerning Urien and his campaigns against the Anglo-Saxons, leaving the date of Urien's death an open question.