McDonald attended Trinity College Dublin, where he graduated with a law degree in 1984.
[5][6][7][8][9] He was involved in several insolvency proceedings during the 1990s, including of the Irish Press, business interests of Larry Goodman and Windmill Lane Studios.
[14] He appeared in the High Court for the Mahon Tribunal against The Irish Times and Bertie Ahern.
[18][19] The case was important in European Union competition law for determining "by object" restrictions in cartels.
[27][28][29][30][31][32] In 2020, he determined an appeal by Perrigo against a decision of the Revenue Commissioners regarding a €1.6 billion tax liability.
[32] McDonald was nominated by Taoiseach Simon Harris's government as a judge of the Court of Appeal on the 31st of October 2024 and was appointed by President Michael D. Higgins on the 1st of November 2024.