In his playing days Reid started off at Dumfries club, Queen of the South where he was signed by Nobby Clark. Reid was later remembered by teammate Tommy Bryce as one of the best players at the club. The three were part of Queen's 1985–86 Scottish Second Division promotion success. It was at Queens where Reid gave his longest service as a player. Reid then played for Clyde and Hamilton Academical before finishing his career with Stirling Albion. He worked as a printer while playing part-time.
Coaching career
Clyde
Reid began his managerial career in 2002 with a caretaker appointment at a club he had played for, Scottish First Division club Clyde. This was in between the departure of Allan Maitland and the appointment of Alan Kernaghan. He took over the Bully Wee on a permanent basis in July 2004 following Kernaghan's two-year spell in charge. Reid took the club to third place in the 2004–05 Scottish First Division in his only season in charge.
Hamilton Academical
Reid then became manager at a club competing in the same division as Clyde and another which he had previously served as a player, Hamilton Academical, taking over from Allan Maitland, also a former Clyde boss. Working under owner Ronnie MacDonald, he took the Accies to the 2007–08 Scottish First Division title earning promotion to the Scottish Premier League. He won that season's PFA ScotlandManager of the Year award. After leading Hamilton to an impressive seventh-place finish in the Scottish Premier League in 2009–10, Reid was linked with a move to a number of clubs including Swansea City, but rejected their approach claiming to have unfinished business with Hamilton. Hamilton were relegated from the top flight in 2011. Reid left Hamilton by mutual consent on 3 April 2013, after more than seven years in the job.
Östersund
Despite being linked to the manager's job at Morton, Reid became assistant manager at Östersund in November 2013 to Graham Potter. At the end of his second year in Sweden Östersunds were runners-up in the 2015 Superettan earning promotion to the top flight. In 2017 they finished fifth in the league and won the 2016–17 Svenska Cupen. This earned a place in the 2nd qualification round of the 2017–18 UEFA Europa League in which they eliminated Galatasaray. They also eliminated PAOK before finishing second in the group behind Athletic Bilbao eliminating Zorya Luhansk and Hertha BSC. They were knocked out in the next round by Arsène Wenger's Arsenal 4–2 on aggregate.
Swansea City
Reid was appointed assistant manager at Swansea City on 11 June 2018, again working with Graham Potter. Swansea finished in 10th place in their first season back in the Championship after relegation from the Premier League. The Swans made the quarter final of the FA Cup controversially losing to Manchester City.
Brighton & Hove Albion
Potter was appointed as the new Brighton & Hove Albion manager on 20 May 2019 where Reid, coach Bjorn Hamberg and head of recruitment Kyle Macaulay moved to the Sussex club alongside Potter.
Personal life
His son, Billy Jnr, was also a footballer, who played for Clyde.
