Cynewulf († 786) was king of the Anglo-Saxon kingdom of Wessex from 757 to 786.
Cynewulf is said to be from the House of Wessex, but this claim may have been made to legitimize his kingship. He belongs to a group of five West Saxon kings from the time between 726 and 802, whose statements of origin are to be regarded with skepticism.
Sigeberht succeeded the late Cuthred on the throne in 756. Soon, however, complaints arose against his style of rule, so that Sigeberht was deposed by the West Saxon Witenagemot and given the rule of Hamtunscir (new king of Wessex became Cynewulf. However, Sigeberht also met resistance as lord of Hampshire. After being accused of murdering Ealdorman Cumbra, his last supporter, he was driven from the land by Cynewulf. He fled to the Weald in the borderlands between the kingdoms of Kent and Sussex. There, after 757, he was murdered at Pryfetesflodan (Privett, Hampshire) by a swineherd who sought to avenge Ealdorman Cumbra.
It appears that Æthelbald of Mercia was able to exercise some degree of authority over Wessex during the period of internal turmoil in Wessex, as he was able to grant land in Wiltshire to the West Saxon abbot of Malmesbury Abbey in 757. One of the witnesses to the charter was King Cynewulf of Wessex. Wiltshire was a disputed territory between Mercia and Wessex. According to other readings, it involved the return of “occupied” territory and Æthelbald”s recognition of Cynewulf as the rightful king. Æthelbald was slain by his bodyguard the same year, resulting in a period of throne turmoil in Mercia, which Cynewulf exploited to gain complete independence for Wessex.
He probably also regained control of Cookham Abbey and parts of Berkshire. He was also able to annex territories north of the River Avon in the neighboring kingdom of Hwicce, which was dependent on Mercia to the northwest. He initially maintained good relations with Offa (757-796), the new king of Mercia. Cynewulf was a benefactor of the church. He donated lands in Somerset, Dorset, and Wiltshire to monasteries, but there is also an example of his keeping landed estates claimed by the Church for himself. He fought several wars against British Cornwall, and at least one gift of land to the church was to support these campaigns through the prayers of the monks. He was in correspondence with Bishop Lullus of Mainz (754-786), a native of Wessex. He promoted the stalled development of the port and trading city of Hamwic (Southampton) and probably initiated coinage there.
In 772 Cynewulf attended a meeting in Sussex between Kings Offa of Mercia and Ecgberht II of Kent with the South Saxon nobles defeated by Offa. Offa could dispose of lands in Sussex as he saw fit. The former kings Oswald (fl. 772), Osmund (fl. 758
In 779 the battle between Offa and Cynewulf took place at Bænesingtun (Benson in Oxfordshire). Cynewulf was forced to retreat and subsequently lost Cookham (Berkshire) and areas of the northeastern borderlands. In 781, as a result of the Synod of Brentford, he had to cede the monastery at Bath and territories on both sides of the River Avon to Offa. Despite these territorial losses, Cynewulf appears to have continued to rule as a fully independent king in his slightly diminished realm. Notwithstanding these conflicts, Cynewulf and Offa attended the Synod of Canterbury together with legates of Pope Hadrian I in 786. In 786 Cyneheard, a brother of the deposed Sigeheard, sought the kingship himself. He attacked Cynewulf at Merentun (probably Marton near Grafton in Wiltshire). Both fell in this battle. Cynewulf was buried at Winchester and Beorhtric succeeded him.