William Martin McKechnie (born 16 April 1951) is an Irish judge who has served as a Judge of the Supreme Court of Ireland since March 2010.
He previously served as Judge of the High Court from 2000 to 2010.
He was educated at Presentation Brothers College, Cork, University College Cork and King's Inns.
He was called to the bar in 1971 and became a Senior Counsel in 1987.
He was elected chairman of the Bar Council in 1999, and was appointed as a Judge of the High Court in 2000.
He holds a Master's degree in European law and presided over competition matters in the High Court from 2004 to 2010.In the High Court, McKechnie made Ireland's first declaration of incompatibility under the European Convention on Human Rights Act 2003 in Foy v An t-Ard Chláraitheoir.In 2010, he was elected President of the Association of European Competition Law Judges, which represents judges from each of the 28 European Union member states.
In June 2010, he was appointed to the Supreme Court, following the retirement of Hugh Geoghegan.