he became king of brega and high king in 675, after killing his predecessor, and first cousin, cenn fáelad in battle at aircheltra, a place which is not identified. the "fragmentary annals of ireland" relate how finsnechta won support by his generosity. among those he won over were the king of fir rois and saint adomnán. according to this annal, he had been granted a stewardship by cenn fáelad, but was unsatisfied with this and encouraged by his friend of fir rois he challenged cenn faelad to battle and won the kingship.