O'Connor comes from a legal family, with his father and grandfather having run a firm of solicitors in Swinford, County Mayo.

[9][10] He appeared for the State against Ali Charaf Damache and acted for Irish Nationwide Building Society.

[21] He has heard cases involving tax law,[22] extradition,[23] insolvency,[24] injunctions,[25] defamation,[26] personal injuries,[27] and commercial disputes.

The truck driver was told over 10 years later that he owed €1.5 million to the Greek authorities which the Irish revenue was obliged to collect under EU law.

[29] The ECJ in 2018 answered the questions posed and, in May 2018, O’Connor granted a declaration that the Irish Revenue could not fulfil the request of the Greek authorities to recover the sum sought.

[33] In July 2020, he was appointed as a member of a three-judge tribunal into the CervicalCheck cancer scandal with chairperson Ann Power and retired judge Brian McGovern.

[35][36] O’Connor delivered judgment for the Court of Appeal in April 2022 which clarified the application of principles under the 2004 EU Citizens Directive.