Tadc mac Briain (died 1023) was the son of Brian Boru and Echrad, daughter of Carlus mac Ailella of Uí Áeda Odba.[1] Tadc had one son, Toirdelbach Ua Briain (Turlough O'Brien), with his wife Mór, daughter of Gilla Brigte Ua Maíl Muaid of Cenél Fiachach.[2]
After Brian Boru's death at the battle of Clontarf in 1014, Tadc was a serious contender to the kingship of Munster, rivalling his half brother Donnchad mac Briain.[3] Tadc was assassinated at the instigation of Donnchad in 1023.[3]