Suibne belonged to the junior branch of the Cenél nEógain kindred of the northern Uí Néill, the Cenél Feredaig, named for his grandfather Feredach, a great-grandson of Niall of the Nine Hostages.
Neither Suibne's father Fiachnae, nor his grandfather, had been kings of Cenél nEógain.
Áed Uaridnach of the Cenél maic Ercae died in 612, and the kingship of the Uí Néill passed to the rival northern Cenél Conaill in the person of Máel Coba mac Áedo.
It is suggested that Suibne Menn's control of the kingship rested on an alliance with another minor Uí Néill kindred, the southern Clann Cholmáin.
In 628 Máel Coba's brother Domnall attacked Suibne, but was defeated and fled.