He was the son of Patrick Segrave (died 1552), head of the prominent landowning family of Killegland, now Ashbourne, County Meath and his wife Joan Beg; the Richard Sydgrave who was Chief Baron of the Irish Exchequer 1423-5, was a direct ancestor.
His aunt Katherine was the second wife of Alderman Robert Ussher of Santry, a member of one of Dublin's most prominent families.
[1] In 1578 he became second Baron of the Court of Exchequer (Ireland) on the suspension of Nicholas Nugent from his office of Chief Justice of the Irish Common Pleas.
The trial gave rise to deep disquiet, due partly to the failure of the Crown to produce two witnesses, as normally required in a treason trial, and partly due to the perceived bias of the judges, especially Sir Robert Dillon, a lifelong enemy of Nugent.
Further, contrary to the modern principle of judicial impartiality, it was said that the judges were actually chosen for their personal knowledge of Nugent.