Sir Paul Walker was born in Wellington, New Zealand, went to school at St Peter's College in Adelaide, South Australia, and studied law at Magdalen College, Oxford, where he was awarded the University's prestigious Eldon Law Scholarship. He was called to the Bar by Gray's Inn in 1979, and became a member of Brick Court Chambers, where he practised both commercial law and public law. From 1994 to 1996, he was a Senior Lecturer in Law at the University of Wellington, and from 1998 to 2000 he was counsel to the BSE Inquiry, which was chaired by former Commercial Judge, Lord Justice Phillips (as he was at the time). Sir Paul was appointed Queen's Counsel in 1999 and sat as a Recorder and as a commercial arbitrator before he became a Queen's Bench Judge in 2004. He was nominated to sit in the Commercial Court in 2007. He was also President of the Administrative Appeal Chamber of the Upper Tribunal from 2009 to 2012.

Sir Paul retired from the High Court in 2019, and returned to practice as a commercial arbitrator. He is a keen musician.