Flaithrí mac Domnaill (died 777)[1] was a King of Connacht from the Uí Briúin branch of the Connachta. He was the son of Domnall mac Cellaig (d.728), a previous king.[2] The sept of Uí Briun he belonged to was the Síl Cellaig of Loch Cime. He reigned from 773-777.
In 775 the Uí Maine were defeated by the Sil Cellaig at the Battle of Achad Liac (in Cluain Acha Liag, now called Killeroran- i.e. the Uí Maine inauguration site). After this battle the law of Ciarán of Clonmacnoise was again imposed on Connacht.[3]
The annals record his death in 777, but other historians state he abdicated and died in 779.[4]