Although born in Belfast, Duff was raised in Bedale, North Yorkshire. As a school boy he represented North Yorkshire and joined the Darlington Football Club School of Excellence before moving to Cheltenham in 1994. Spotted by Cheltenham Town scout Derek Bragg playing for Carterton Town, Duff was invited by Mike Davis, youth team manager to join Cheltenham, then playing in the Southern League. He had a spell on loan at Cirencester Town before returning to Cheltenham when Steve Cotterill took over as manager. He became a regular for Cheltenham, and went on to play 242 games and score 15 times, including a 93rd-minute winner in a 3–2 victory at home to Yeovil Town in 1999 that secured Cheltenham Town promotion to the Football League. On 5 July 2004, he made a £30,000 switch to Burnley where he became a regular, if not always automatic, first-team choice. Over the next couple of seasons he established himself as first choice right-back, although he had equally often played at centre-back. His first Burnley goal was credited in a League Cup game against Carlisle United, even though it might equally have been credited as an own goal. He finally got incontrovertibly on the score-sheet on 14 October 2006 against Hull City. Duff was part of two of Northern Ireland's finest international moments of recent years; as a late substitute in their 1–0 victory over England on 7 September 2005 and then in a 3–2 victory over Spain on 6 September 2006. In the 2007–08 season Duff picked up a serious injury during the Championship match against Crystal Palace at Turf Moor. The injury ruled Duff out for almost a year, causing him to miss the first half of the following campaign. He suffered multiple ligament damage and hamstring damage as well as a cruciateknee injury. Duff started his first Premier League match on Boxing Day 2009 against Bolton Wanderers at Turf Moor, having made his debut as a substitute in the preceding game versus Wolverhampton Wanderers. In doing so, he completed the rare feat of having played in each of the top eight tiers of English football in ascending order during his career: the Hellenic League with Carterton Town, the Southern League with Cirencester Town, the Southern League, Conference, League Two and League One with Cheltenham Town, and the Championship and Premier League with Burnley. After Burnley's relegation, Duff remained with the team and, over the next three seasons, was a frequent, though not automatic, first team choice as injuries and competition for places saw him play in roughly half of Burnley's league matches in each of the seasons through this period. By the summer of 2013, having earned a season extension for 2013–14 on the basis of his appearances, Duff was the longest-serving player at the club. On 2 July 2014, Duff signed a new one-year contract with Burnley, Duff remained the only survivor of the squad that reached the Premier League in 2009 and his final deal meant the former Northern Ireland international entered his 11th season with the club. Duff retired from playing professionally at the end of 2015–16 season, having helped Burnley win the Championship title and promotion to the Premier League. As a result of this, Duff became the first footballer to be promoted to the Premier League on three occasions with the same club.
Managerial career
On 10 September 2018, Duff was appointed to his first managerial appointment at his former club Cheltenham Town in League Two. He was awarded the League Two Manager of the Month award for September 2019 and February 2020. On 1 November 2019, Duff signed a contract extension which will keep him at Cheltenham Town until June 2023.
