 He fought Bécc Bairrche mac Blathmaic (d. 718), King of Ulster, in 679 at the Battle of Tailtiu.In June 684, Ecgfrith, the King of Northumbria, sent an army under Berht to Ireland which laid waste to the plain of Brega, the heart of Fínsnechta's kingdom.The reasons for the sending of the army are unclear.