The earliest version of the Anglo-Saxon Chronicle, the Parker Chronicle, begins with a genealogical preface tracing the ancestry of Ecgberht's son Æthelwulf back through Ecgberht, Ealhmund (thought to be king Ealhmund of Kent), and the otherwise unknown Eafa and Eoppa to Ingild, brother of King Ine of Wessex, who abdicated the throne in 726.

[3] Heather Edwards in her Oxford Dictionary of National Biography article on Ecgberht argues that he was of Kentish origin and that the West Saxon descent may have been manufactured during his reign to give him legitimacy,[4] whereas Rory Naismith considered a Kentish origin unlikely, and that it is more probable that "Ecgberht was born of good West Saxon royal stock".

A fifteenth-century chronicle now held by Oxford University names her as Redburga, supposedly a relative of Charlemagne whom he married when he was banished to Francia, but this is dismissed by academic historians in view of its late date.

[12] The extent of Offa's control of Kent between 765 and 776 is a matter of debate amongst historians, but from 776 until about 784 it appears that the Kentish kings had substantial independence from Mercia.

There is, however, the extensive evidence of Offa's domination of Kent during the late 780s, with his goals apparently going beyond overlordship to outright annexation of the kingdom,[12] and he has been described as "the rival, not the overlord, of the Kentish kings".

[16][17] The Anglo-Saxon Chronicle records that Ecgberht spent three years in Francia before he was king, exiled by Beorhtric and Offa.

This requires assuming that the error in transcription is common to every manuscript of the Anglo-Saxon Chronicle; many historians make this assumption but others have rejected it as unlikely, given the consistency of the sources.

[19] At the time Ecgberht was in exile, Francia was ruled by Charlemagne, who maintained Frankish influence in Northumbria and is known to have supported Offa's enemies in the south.

[21] The Mercians continued to oppose Ecgberht: the day of his accession, the Hwicce (who had originally formed a separate kingdom, but by that time were part of Mercia) attacked, under the leadership of their ealdorman, Æthelmund.

[14][24] Ten years later, a charter dated 19 August 825 indicates that Ecgberht was campaigning in Dumnonia again; this may have been related to a battle recorded in the Chronicle at Gafulford in 823, between the men of Devon and the Britons of Cornwall.

[26] The Chronicle tells how Ecgberht followed up his victory: "Then he sent his son Æthelwulf from the army, and Ealhstan, his bishop, and Wulfheard, his ealdorman, to Kent with a great troop."

The relevant part of the annal reads, in the C manuscript of the Chronicle:[29] ⁊ þy geare geeode Ecgbriht cing Myrcna rice ⁊ eall þæt be suþan Humbre wæs, ⁊ he wæs eahtaþa cing se ðe Bretenanwealda wæs.In modern English:[30] And the same year King Egbert conquered the kingdom of Mercia, and all that was south of the Humber, and he was the eighth king who was 'Wide-ruler'.The previous seven bretwaldas are also named by the Chronicler, who gives the same seven names that Bede lists as holding imperium, starting with Ælle of Sussex and ending with Oswiu of Northumbria.

The exact meaning of the title has been much debated; it has been described as "a term of encomiastic poetry"[31] but there is also evidence that it implied a definite role of military leadership.

[33] According to a later chronicler, Roger of Wendover, Ecgberht invaded Northumbria and plundered it before Eanred submitted: "When Ecgberht had obtained all the southern kingdoms, he led a large army into Northumbria, and laid waste that province with severe pillaging, and made King Eanred pay tribute."

[34] However, the nature of Eanred's submission has been questioned: one historian has suggested that it is more likely that the meeting at Dore represented a mutual recognition of sovereignty.

This demonstration of independence on East Anglia's part is not surprising, as it was Æthelstan who was probably responsible for the defeat and death of both Beornwulf and Ludeca.

[25] Both Wessex's sudden rise to power in the late 820s, and the subsequent failure to retain this dominant position, have been examined by historians looking for underlying causes.

At Easter 839, not long before Ecgberht's death, he was in touch with Louis the Pious, king of the Franks, to arrange safe passage to Rome.

However, the Rhenish and Frankish commercial networks collapsed at some time in the 820s or 830s, and in addition, a rebellion broke out in February 830 against Louis the Pious—the first of a series of internal conflicts that lasted through the 830s and beyond.

In this view, the withdrawal of Frankish influence would have left East Anglia, Mercia, and Wessex to find a balance of power not dependent on outside aid.

[41] Mercia remained a threat, however; Ecgberht's son Æthelwulf, established as king of Kent, gave estates to Christ Church, Canterbury, probably to counter any influence the Mercians might still have there.

The Dumnonian royal line continued after this time, but it is at this date that the independence of one of the last British kingdoms may be considered to have ended.

[45] Both the record of the Council of Kingston, and another charter of that year, include the identical phrasing: that a condition of the grant is that "we ourselves and our heirs shall always hereafter have firm and unshakable friendships from Archbishop Ceolnoth and his congregation at Christ Church.

[45] The kingship of Wessex had been frequently contested among different branches of the royal line, and it is a noteworthy achievement of Ecgberht's that he was able to ensure Æthelwulf's untroubled succession.

[45] In addition, Æthelwulf's experience of kingship, in the subkingdom formed from Ecgberht's southeastern conquests, would have been valuable to him when he took the throne.

[48] Ecgberht was buried in Winchester, as were his son, Æthelwulf, his grandson, Alfred the Great, and his great-grandson, Edward the Elder.