McFarlane was called to the bar at Gray's Inn in 1977 and has been a Bencher since 2003. He began his pupillage in London at chancery chambers before moving to 2 Fountain Court in Birmingham (now St Philips Chambers). While there, he and David Hershman wrote Hershman and McFarlane: Children Law and Practice. He then moved to 1 King’s Bench Walk in Temple, London in 1994.[2] In 1998, he became a Queen's Counsel.
He was appointed an Assistant Recorder in 1995, a Recorder in 1999 and a deputy High Court Judge in 2000. He was appointed as a judge of the High Court of Justice on 18 April 2005[5] and assigned to the Family Division, receiving the customary knighthood. McFarlane was the Family Division Liaison Judge for the Midland Circuit from 2006 until his appointment as a Lord Justice of Appeal[6] on 28 July 2011,[7] whereupon he received the customary appointment to the Privy Council. On 28 July 2018, he was appointed President of the Family Division.[8]
He was, until January 2019, the President of Tribunals and Chair of the Clergy Discipline Commission of the Church of England under the Clergy Discipline Measure 2003.[9]