[1] Sechnassach's father and uncle are said to have died in a great plague—the buide Chonaill—which struck Ireland from 664 or 665 onwards.
[2] While the Baile Chuinn Cétchathaigh, compiled in the reign of Fínsnechta Fledach (died 695), does not include Sechnassach or his brother Cenn Fáelad (died 675) among its High Kings, the Chronicle of Ireland, on which other Irish annals were founded, named him as a High King on his death.
His only recorded marriage was with one Findelb ingen Chellaig, who may have been a daughter of Cellach Cualann (died 715).
He was killed in November 671 by Dub Dúin, king of Cenél Coirpri, a minor Uí Néill kingdom on the upper reaches of the River Boyne near Clonard.
[6]He has appeared in both the novels and short stories of Peter Tremayne's Sister Fidelma mysteries.