After studying catering at a technical college, Platt worked first for Trust House Forte, and then in administration for the BBC.
After multiple attempts to work on the series, he wrote the 1989 Doctor Who serial Ghost Light based on two proposals, one of which later became the novel Lungbarrow.
That novel was greatly anticipated by fans as it was the culmination of the so-called "Cartmel Masterplan", revealing details of the Doctor's background and family.
After the original series' cancellation, Platt wrote multiple tie-in novels for Virgin Publishing, and later would become a regular writer for Big Finish Productions.
Among his most famous productions was the audio Doctor Who drama Spare Parts, which told the origin of the Cybermen.