Ferriter attended secondary school at St Benildus College in Kilmacud, County Dublin, until 1986.
[2] He was the auditor of the University College Dublin Law Society between 1991 and 1992 and was the individual winner of the Irish Times Debate in 1992.
[22][23] He was counsel for John Gilligan in a 2003 appeal to a conviction for possession of drugs for supply and for Thomas Murphy in 2007 in a challenge against the Criminal Asset Bureau.
[26][27] He was counsel for Tomasz Zalewski in the Supreme Court of Ireland who successfully challenged the constitutionality of aspects of the Workplace Relations Commission.
[28] Ferriter frequently appeared in defamation cases, acting for RTÉ in actions taken by the politicians Beverley Flynn and Joe Costello, for Independent News & Media against Monica Leech and for The Irish Times against Maurice McCabe.