Probably born at the Imperial Frankish Court in Aachen, Aethelwulf was the eldest son of King Egbert of Wessex and his wife, Redburga. He was the commander of the Wessex army which conquered Kent in AD 825 and, upon the submission of Essex, Sussex and Surrey, he became sub-King of all his father's South-Eastern lordships. Fourteen years later, he succeeded Egbert as King of All the English and his sub-kingdom was handed over to his own son, Aethelstan.

During Aethelwulf's reign, Viking incursions into Wessex stepped up a notch. Like his father, Aethelwulf was unsuccessful in battle at Carhampton, against the crews of thirty-five Viking Ships in AD 843. According to the Anglo-Saxon Chronicle, eight years later, the West Saxons "inflicted the greatest slaughter on a heathen army". They recovered their dominance in the field, first at the Battle of Aclea (thought to be Water Oakley in Berkshire) under Aethelwulf's second son, Aethelbald; and, subsequently, in a sea-battle off Sandwich, under his eldest son, Aethelstan, who died later that same year. It was probably this Viking threat which led to a newfound accord between the old enemies of Wessex and Mercia. In 853, King Burgred of Mercia asked for Aethelwulf's assistance in a campaign against the Welsh, and their alliance was sealed by his marriage to the latter's daughter, Princess Aethelswith. The long contested lands of Berkshire passed permanently into Wessex hands at this time and were probably part of the marriage settlement.

By 855, Aethelwulf was in his fifties and feeling his age. He decided to go on a pilgrimage to Rome, possibly with the intention of retiring there like other monarchs had done before him. He left Wessex in the safe hands of his eldest surviving son, Aethelbald, and the south-east in those of his third son, Aethelbert. The old King did return home, however, stopping at the court of King Charles the Bald of the Franks on the way. The two must have talked extensively of their common troubles caused by the marauding Vikings: a bond which led agree upon a formal alliance by which Aethelwulf's married Charles's fourteen-year-old daughter, Judith. The King of Wessex even accepted the condition that his new wife be actually crowned as queen, despite this being contrary to West Saxon tradition.

Aethelbald was not overjoyed to have his father arrive back in England to reclaim his crown. Especially since he now had a young wife who might bare him more rivals to the throne. The prince had ardent supporters, particularly in Western Wessex, where Ealdorman Enwulf of Somerset and Bishop Aelfstan of Sherborne encouraged him to hold on to his position. Rejected by Wessex, Aethelwulf retired to Aethelbert's provinces in the South-East. He died in AD 858 and was buried at Steyning in Sussex (but was later removed to Winchester). By his first wife, Osburga, the daughter of a Kentish nobleman named Oslac, he had at least six children. Apart from those already mentioned, he was also survived by his younger sons, Aethelred and Alfred.