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". He heard the "Miss D" case in 2007, where he determined that a seventeen year old girl in care could travel to the United Kingdom to obtain an abortion. An editorial in the "Irish Examiner" said the decision was "compassionate, sympathetic and landmark". Also in 2007, he decided in the "Mr. G" case that an unmarried father had a right to withhold or give consent before their child is removed from the country. The Supreme Court upheld the decision. He heard a challenge to the legality of the Twenty-eighth Amendment of the Constitution of Ireland in 2009.