Derek John Walker carved out a reputation in New Zealand cricket long before he ever made a decision from behind the stumps. Born in Dunedin on 23 November 1959, the left-handed batsman and right-arm medium bowler spent his early years representing Otago age-group sides. He even crossed the globe to play for the Nottinghamshire Second XI during the 1980 English summer before returning home to make his senior debut for Otago in December of that year.
Throughout the 1980s, Walker became a permanent fixture in the Otago provincial side. He played 71 senior matches for the team, establishing himself as a reliable all-rounder. Over his playing career, he racked up 1,562 first-class runs at an average of 28.92, hitting two centuries and eight half-centuries, with a top score of 113. He also spent the 1984 English season playing for Cambridgeshire.
As a bowler, Walker rolled his arm over for 1,608 deliveries, claiming 19 wickets with a career-best of four wickets for 50 runs. He also showed safe hands in the field by taking 25 catches. After his playing days on the domestic circuit ended, Walker traded his bat for a white coat, embarking on a long career as a professional umpire.
Walker eventually rose to the International Panel of Umpires and Referees, where he stood in major international fixtures. He officiated nine men's One Day Internationals between 2014 and 2016 and eight men's T20 Internationals from 2013 to 2016. On the women's international stage, he stood in 18 One Day Internationals between 2008 and 2022, as well as six T20 Internationals between 2011 and 2018. His time on the international panel concluded in June 2016 when he joined New Zealand's national umpiring panel.