Ceolwulf ruled autonomously as the King of Mercians, according to historical sources and coinage from the period. There are two records in Ceolwulf's name from 875 that allude to him as the King of Mercians. Mercian bishops and nobility also signed these charters.
Another record mentions a donation made by Ceolwulf, who is still referred to as King. Ceolwulf's name appears on three different kinds of coins. The Cross and Lozenge penny was created as a consequence of a monetary reform carried out by both Alfred and Ceolwulf.
Even though Alfred preferred working with his brother-in-law Burgred and subsequently his son-in-law Thelred, it is apparent that in the 870s, both Mercians and West Saxons accepted Ceolwulf as Mercian ruler.
After the Viking settlement in 877, Ceolwulf retained control of certain parts of Mercia, implying that he was a better negotiator than the Anglo-Saxon Chronicle writer recalled. Ceolwulf II was the final Mercian king.
Burgred's predecessor was driven away by the Vikings in late 873 or early 874. According to the Anglo-Saxon Chronicle, Ceolwulf was a stupid king's servant who became king as a result of the Vikings.
The only other occasion on which Ceolwulf appears in English narrative sources is in 877, when a Viking force went into Mercia and split it, taking half and leaving the remainder for Ceolwulf.
According to a list of Worcester kings, Ceolwulf controlled the western half of Mercia, including Worcester, for two years following the Viking occupation. He was most likely the commander of the English troops who assassinated Rhodri Mawr, King of Gwynedd, in 878.
After 879, nothing is known about Ceolwulf. Thelred was the next name on the Worcester list. By 883, Thelred was the monarch in charge of Mercia under Alfred, who was ascending to the throne of the Anglo-Saxons as a whole, not just the West Saxons.
The Mercians' autonomous kingdom no longer existed. The Chronicle mocks Ceolwulf, calling him a dumb servant who functioned as a caretaker for the Vikings, keeping the land ready for them whenever they needed it.