Darby started out as a goalkeeper for Liverpool Schools and FA Youth Team but never made it professionally and subsequently ended up at Tranmere Rovers before playing for teams in the United States and Australia.
Darby obtained his UEFA A Licence in 1979. He became an official FIFA Instructor for the Oceania region in 1981 and AFC Instructor 1998 and was National Development Manager for the Australian Soccer Federation between 1990-1995.
At the end of his Home United contract, Darby was heavily linked to the vacant India manager's post. However, he did not take up that job, choosing instead to join Perak despite having offers from two other Malaysian clubs and a Vietnamese club.
He led Perak to a second spot in the league 2006-07 season and to the Malaysia Cup final and an AFC Quarter final.The furthest a Malaysian club had gone in Asian Competitions at that time.
In October 2008, he was appointed as Thailand assistant coach and works together with Peter Reid who was appointed Thailand chief coach in August. He would stay on as assistant coach to the newly appointed Bryan Robson as his assistant and as the U-23 Team Coach, after previous coach Peter Reid left to become Stoke manager Tony Pulis assistant.
In September 2013, Darby has been appointed as Kelantan head coach after previous coaches contract expires. He familiar with Malaysian football as previously coached Johor and Perak. He was sacked by Kelantan FA after disappointing 0-4 defeat at the hand of Sime Darby F.C.
Darby holds a Bachelor (Hons) in Physical Education from the University of Leeds and Post Graduate qualifications in Sports Administration from the University of Canberra. He also holds a TEFL Certificate from Cambridge. He speaks Arabic, French and a little Malay. He is married to Nguyen Thi Van Anh. Their daughter, Quinn Elsa, was born in 2005.