As a manager, Platt's first job was to take charge of Ballymena United for a season from 1984–85, after which he had a longer spell at Coleraine, managing them for six years from 1985 to 1991. In 1991 he had another short spell, this time at Ballyclare, for just one season from 1991–92.
For the 1992–93 season, Platt was given the job of managing Swedish outfit Assyriska, in the Swedish First Division. He had a two-season spell managing Darlington one partly with David Hodgson then the other from 1995–96, before leaving full-time management to take a job with Gateshead.
Previously Middlesbrough’s Chief Coach at their Football Community Centre. He ran a private football school for local primary school around the Middlesbrough/Stockton Area.
In May 2009, Platt was appointed as Darlington's goalkeeping coach. However, three months later, Platt left the club following manager Colin Todd's sacking.