The Lebor Gabála Érenn says he reigned jointly with Conaing Bececlach, ruling the southern half of the island while Conaing ruled the north, after he killed the previous southern ruler, Conaing's brother Eochu Fíadmuine, while Keating and the Four Masters say he deposed Conaing when he killed Eochu and ruled the whole island. He ruled for seven years, after which Conaing killed him and became High King of the whole island. The Lebor Gabála synchronises Lugaid's reign with those of Artaxerxes I and Darius II (423-404) of Persia. The chronology of Keating's Foras Feasa ar Éirinn dates his career to 616-609 BC, that of the Annals of the Four Masters to 839-832 BC.