Nial Fennelly (born 3 May 1942) is a retired Irish judge who served as a Judge of the Supreme Court from 2000 to 2014, Advocate General of the European Court of Justice and a Judge of the European Court of Justice from 1995 to 2000. Fennelly is the sole member of the "Commission of Investigation (Certain Matters relative to An Garda Síochána and other persons)", commonly called the Fennelly Commission, a commission of investigation established in April 2014 by the Government of Ireland to investigate several controversies involving the Garda Síochána.