Is married to Dolores Hardcastle (born Dolore Baker) and they have 3 children: Maxine Hardcastle, Paul Hardcastle Jr. and Richard Hardcastle. Susan Hardcastle is Paul's younger sister and she lent her voice to the backing vocals for the song "Fooling Yourself".
Enjoyed success on the underground dance scene in the early 80s before breaking into the mainstream with "19", an international smash which spent five weeks at number one in the UK. In the latter half of the 1980s he specialised in TV soundtrack work, and now records mainly under the pseudonym The Jazzmasters.
Due to contractual reasons, Paul was unable to release music under the Hardcastle name. So, in October 1990, under the pseudonym The Deff Boyz, he released a 12" single entitled The Deff Boyz Featuring Tony Mac - Swing, which crashed in at #4 on Billboards 12" sales chart and was a massive hit all over Europe. Another project under the name LFO also saw massive sales. Even though he was making records that were resulting in millions of sales, Paul had still not found the true direction he had been looking for.
In 1997, Paul did some work for the movie "Spice World"