He was the grandson of Conall Guthbinn mac Suibni (died 635), a previous king.
[2][3] His father Airmetach Cáech[4] was slain at the Battle of Mag Rath in 637.
[6] The feud between Clann Cholmáin and the Síl nÁedo Sláine of the early 7th century had ended in victory for the Síl nÁedo Sláine who dominated the high kingship of Ireland in the second half of the 7th century.
[7] Diarmait himself was killed in 689 as part of the old feud by Áed mac Dlúthaig (died 701) of the Fir Cúl Breg sept of Síl nÁedo Sláine.
[8] According to the Book of Leinster, Conall Guthbinn was killed by the High King Fínsnechta Fledach mac Dúnchado (died 695) of Brega.