Uuen was a son of Onuist II [son of] Uurguist [Wrguist] (in Gaelic: Óengus II mac Fergusa, died 834) and succeeded his cousin Drest mac Caustantín as king in 836 or 837. The sole notice of Uuen in the Irish annals is the report of his death, together with his brother Bran and "Áed mac Boanta, and others almost innumerable" in a battle fought by the men of Fortriu against Vikings in 839. This defeat appears to have ended the century-long domination of Pictland by the descendants of Onuist I [son of] Wrguist (in Gaelic: Óengus I mac Fergusa.
If the annalistic record is short, there are other traditions relating to Uuenn. He is named by the St Andrews foundation tale as one of the sons of Onuist who met with Saint Regulus at Forteviot when the Saint supposedly brought the relics of Saint Andrew to Scotland. Along with his uncle Caustantín, Uuen appears to have been a patron of the Northumbrian monasteries as he is named in the Liber Vitae Dunelmensis, which contains a list of those for whom prayers were said, dating from around 840.
Uuen, his father, his uncle and his cousin Domnall appear in the Duan Albanach, a praise poem from the reign of Máel Coluim (III) mac Donnchada listing Máel Coluim's predecessors as kings of Scots, of Alba and of Dál Riata from Fergus Mór and his brothers onwards. Their inclusion in this source and its like is thought to be due to their importance to the foundation traditions of Dunkeld and St Andrews.
On Uuen's death the Pictish Chronicle king lists have him followed by the short reigns of Uurad (Ferat) and Uurad's sons Bridei, Cináed and Drest, by Bridei son of Fochel (Uuthoil) and, the eventual victor and founder of a new ruling clan, by Cináed mac Ailpín (Ciniod [son of] Elphin).