Simpson - formerly head of press and PR at BBC Radio 1 - will launch the as-yet-unnamed agency in September.
It is understood that the head of comms position at the Children and Young People's Unit remains vacant, although an appointment is expected within a fortnight.
Simpson said he would look to continue working on PR efforts targeting the youth market: 'Basically, I will be trying to use my experience in Whitehall and at Radio 1 to help clients better engage and relate to young people.'
Although he is currently on holiday before the launch, Simpson has already been hired by music service Shazam, for which he has been providing 'strategic advice'.
The service enables consumers to identify music by dialling a number from their mobile phone and playing a 15-second sample of a song down the line. The service then sends a text message to the phone with the name of the track and the artist.
Shazam already retains Mantra PR on B2B and trade work, Hall or Nothing on consumer print media and Anglo Plugging on broadcast media.
All three agencies, and Simpson, report to marketing executive Mekhala Chatterjee.