Reed started his coaching career in non-league football, coaching both Finchley and Wealdstone. In 1985 Wealdstone won both the Football Conference and the FA Trophy with him. In 1986, he joined the Football Association as development officer. He worked there for nine years in a variety of roles including Regional Director of Coaching and coach at The FA National School, where he worked with Joe Cole, Sol Campbell, Nick Barmby and Michael Owen, among others. He went to Italy for his first World Cup in 1990 with Bobby Robson's England team. It was the first of three World Cup finals tournaments in which he would serve his country. In 1995 Reed left the FA to become Alan Curbishley's assistant at Charlton Athletic, helping them to gain promotion to the FA Premier League via the playoffs in 1998. After the final Reed was appointed Director of Technical Development at the FA by Howard Wilkinson, its Technical Director at the time. He coached England's new under-15 National Team to win the Nationwide Trophy at Wembley, defeating an Argentine team that included Carlos Tevez.
In 1998 Reed rejoined the FA as part of the England national coaching setup under Kevin Keegan. During Euro 2000, Keegan allowed Reed to respond to virtually all the tactical questions posed by the English press after England's defeat by Portugal. Many journalists wondered in their columns how a manager and his coaching team had allowed a minor member of their entourage such an important role. In his autobiography, Gerrard: My Autobiography, Liverpool captain Steven Gerrard said that he had "no respect" for Les Reed after the way he treated him during England's Euro 2000 campaign. Gerrard wrote, "To this day, I have no respect for Reed or Derek Fazackerley. I was a young lad who had never been away from home to play football before. They didn't seem to understand that not everyone can board a plane, settle in a strange hotel far from the family they love, and find it easy. In fact they made me feel like shit. My homesickness worsened whenever I was forced to be in their company. I felt they could have shown more care and sympathy. They were always pushing me, always telling me to buck up my ideas." In 2002 Reed replaced Howard Wilkinson as the FA's Technical Director. During his second spell at the FA he authored the FA's official coaching manual, The Official FA Guide to Basic Team Coaching, but he was sacked by the FA in 2004.
Charlton Athletic
Reed worked for a time as a consultant. Among his clients was the Northern Ireland national football team, who would beat England during his stint with the side. He returned to Charlton to become Iain Dowie's assistant manager in summer 2006. Dowie was sacked on 14 November 2006 and Reed was promoted to replace him. During his six-week spell as manager Reed managed just one victory, and Charlton were knocked out of the League Cup by League Two team Wycombe Wanderers. Reed's spell at Charlton became infamous, as the media attacked him frequently, nicknaming him "Les Misérables" and "Santa Clueless", and he was later voted in an unofficial online poll "the worst manager of all time". He was replaced as manager by Alan Pardew on 24 December, leaving Charlton Athletic by mutual consent.
Reed was linked with a consultancy role helping Northern Ireland boss Lawrie Sanchez, who approached him after a League Managers' Association meeting at West Bromwich Albion in February 2007. He had been considering consultancy roles with the football associations of Turkey and Latvia, and he revealed that he could return to Charlton in an overseas development role. After a period advising the Football Association of Ireland, he became first-team coach at Fulham in April 2007, where he helped the club retain their league position at the expense of Charlton. In June 2007 he was appointed Director of Football at Fulham, notably recruiting Chris Smalling from non-league football, later to be sold for an estimated 12 million pounds to Manchester United.
On 19 December 2008 Reed was appointed assistant manager on a voluntary basis at Bishop's Stortford in the Conference South, to help manager Mark Simpson, a long-standing friend. Here he was instrumental in recommending winger Danny Green to John Still, manager of Dagenham and Redbridge F.C.
Southampton
On 16 April 2010 Reed was appointed Head of Football Development and Support at Southampton, and later the Vice-Chairman, overseeing four main areas: the Youth Academy, Scouting and Recruitment, Sports medicine and Science, and Kit and Equipment Management. Reed left the club on 8 November 2018.
Football Association
On 21 December 2018, It was announced that Reed was appointed as the Football Association's technical director, and would take up the post in February 2019.
