He is also known as Ursellus de Ballione in Latin or Roscelin or Roskelin de Baieul, and Anna Comnena called him Urselius. Roussel was possibly a Frank, but certainly ventured with the Apulian Normans to Italy, settled in Terra d"Otranto and served under Roger de Hauteville in Sicily. According to Geoffrey Malaterra, Roussel distinguished himself with his bravery at the Battle of Cerami, where he urged Count Roger to pursue the fleeing Saracens.
Aside from this brief account by Malaterra, The Alexiad of Anna Comnena is the main source for Roussel.
He was present at the Battle of Manzikert in 1071, where he refused to join the fray, which proved to be a disastrous defeat for the Byzantines. Despite this treachery, he was kept in imperial service, where good generals were needed, and was sent into Asia Minor again with a force of 3,000 Franco-Norman heavy cavalry.
There Roussel conquered some territory in Galatia and declared it an independent state, in 1073, with himself as prince, following the example set by his fellow Normans in the Mezzogiorno. His capital was Ankara, now the capital of Turkey.
He defeated the Caesar John Ducas and sacked Chrysopolis, near Constantinople.
He even supported a usurper candidate, but by formally ceding lands that the Seljuk Turks had actually conquered, the emperor Michael VII persuaded the Seljuk warlord Tutush I to remove Roussel. However, the Norman evaded imperial would-be captors and found refuge in Amasea, where the population so loved him that he made himself undisputed governor. He was given up by the people through a ploy of Alexius Comnenus (1074), then a general, later an emperor.
In 1077, he was released (for a ransom) from his Constantinopolitan imprisonment to lead a battalion against the rebel Nicephorus Botaniates.
He defeated him handily, but then played the traitor and joined him. This time, the emperor called up the Seljuks again and they defeated and captured him at Nicomedia.
He was given over to Byzantium and executed.