[2] He served a term as the chair of the professional practices committee of the Bar Council, and was a member of the Commission on the Private Rented Residential Sector, the Valuation Tribunal and the Courts Service Board.
[15][16] 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.
[22] His decision in Digital Rights Ireland v. Minister for Communications clarified the rules of standing, outlining criteria required for a company to pursue an actio popularis.
In 2015, in DPP v. JC he formed the minority with John L. Murray and Adrian Hardiman, declining to depart from previous court decisions regarding the exclusionary rule in Ireland.
[33] He disagreed with six other judges of the Supreme Court in 2017 in DPP v Doyle by holding that people in custody had a right of access to a solicitor during questioning.
[34] In Persona Digital Telephony Ltd v. Minister for Public Enterprise, Ireland he wrote the sole dissent from the majority regarding the position of champerty and maintenance in Irish law.
[35] The approach of McKechnie in Gorry v. Minister for Justice and Equality, where he held that there was a constitutional right for spouses to cohabit, was not adopted by his colleagues.